Magnetic composites and methods for improved electrolysis

ABSTRACT

Magnetic composites exhibit distinct flux properties due to gradient interfaces. The composites can be used to improve fuel cells and batteries and effect transport and separation of different chemical species. Devices utilizing the composites include an electrode and improved fuel cells and batteries. Some composites, disposed on the surface of electrodes, prevent passivation of those electrodes and enable direct reformation of liquid fuels. Methods involving these composites provide distinct ways for these composites to be utilized.

RELATED APPLICATION

This application is a Continuation of application Ser. No. 09/239,156filed Jan. 28, 1999, (now U.S. Pat. No. 5,981,095) which is a Divisionalof application Ser. No. 08/659,505, filed Jun. 6, 1996 (now U.S. Pat.No. 5,871,625), which is a continuation-in-part of application Ser. No.08/294,797, filed Aug. 25, 1994 now abandoned. Application Ser. No.08/659,505 is also a continuation-in-part of application Ser. No.08/486,570, filed Jun. 7, 1995 now U.S. Pat. No. 6,001,248 and acontinuation-in-part of Ser. No. 08/597,026, filed Feb. 5, 1996 now U.S.Pat. No. 5,817,221.

Part of the work performed during the development of this inventionutilized U.S. government funds under grants No. CHE92-96013 and No.CHE93-20611 from the National Science Foundation, Chemistry Division,Analytical and Surface Science. The government may have certain rightsin this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a method for forming and exploitinggradients at the interfaces between components of a composite material,as well as to the composite material itself, and devices whichincorporate the material. In particular, the invention relates to amethod for forming and exploiting magnetic gradients at the interfacesbetween components of a magnetic composite material and the magneticcomposite material itself as well as devices which incorporate thecomposite material such as electrochemical systems and separatorsincluding fuel cells, batteries, and separations resulting in enhancedand modified flux and performance in those systems. The inventionfurther relates to compositions, apparatus, methods of making, andmethods of using magnetic composite materials in electrolyticapplications, including fuel cells. In particular, the invention relatesto compositions, apparatus, methods of making, and methods of usingmagnetic composite materials in electrolytic applications to preventelectrode passivation, particularly in fuel cell applications for thedirect reformation of fuels; and to apparatus and methods for modifyingthe outcome of electrolyses involving free radical products andintermediates.

As used herein, the term “fuel” includes mixtures of one or more fuels,either liquid or gaseous, with other fuel or non-fuel components,including fuel mixtures of one or more fuels with air. As used herein,the term “fuel mixture” refers to a mixture of a fuel with one or moredifferent fuel, or non-fuel, components.

2. Background of the Related Art

In the detailed description of preferred embodiments, it will be shownthat interfacial gradients in properly prepared composite materials canbe exploited to enhance flux in many types of electrochemical systemssuch as fuel cells, batteries, membrane sensors, filters and fluxswitches. Such interfacial gradients may also be exploited in separatorsinvolving chromatographic separations and nonelectrochemical separationsincluding, but not limited to, separations of light and heavy transitionmetals and transition metal complexes. The heavy transition metalsinclude the lanthanides and the actinides which have atomic numbers58-71 and 90-103, respectively. First, however, the following discussionprovides a brief overview of the current understanding of magneticproperties in composites. In particular, the discussion below summarizesthe thermodynamic, kinetic and mass transport properties of bulkmagnetic materials. These bulk properties of molecules in magneticfields are fairly well understood.

Rudimentary Magnetic Concepts

Paramagnetic molecules have unpaired electrons and are attracted into amagnetic field; diamagnetic species, with all electrons paired, areslightly repelled by the field. Radicals and oxygen are paramagnetic;most organic molecules are diamagnetic; and most metal ions andtransition metal complexes are either para- or diamagnetic. How stronglya molecule or species in a solution or fluid responds to a magneticfield is parameterized by the molar magnetic susceptibility, χ_(m)(cm³/mole). For diamagnetic species, χ_(m) is between (−1 to −500)×10⁻⁶cm³/mole, and temperature independent. For paramagnetic species, χ_(m)ranges from 0 to +0.01 cm³/mole, and, once corrected for its usuallysmall diamagnetic component, varies inversely with temperature (Curie'sLaw).

While ions are monopoles and will either move with or against anelectric field., depending on the sign of the ion, paramagnetic speciesare dipoles and will always be drawn into (aligned in) a magnetic field,independent of the direction of the magnetic vector. These dipoles willexperience a net magnetic force if a field gradient exists. Becauseelectrochemistry tends to involve single electron transfer events, themajority of electrochemical reactions should result in a net change inthe magnetic susceptibility of species near the electrode.

Magnetic field effects on chemical systems can be broken down into threetypes: thermodynamic, kinetic, and mass transport. Macroscopic,thermodynamic effects are negligible, although local magnetic fieldeffects may not be. Kinetically, both reaction rates and productdistributions can be altered. Transport effects can lead to fluxenhancements of several-fold. Quantum mechanical effects are alsopossible, especially on very short length scales, below 10 nm. Thefollowing summarizes what has been done with homogeneous fields appliedto solutions and cells with external laboratory magnets.

Thermodynamics

A magnetic field applied homogeneously by placing a solution between thepoles of a laboratory magnet will have a negligible nonexponentialeffect on the free energy of reaction. ΔG_(m)=−0.5Δχ_(m)B² J/mole, whereΔG_(m) is the change of the free energy of reaction due to the magneticfield, Δχ_(m) is the difference in magnetic susceptibility of theproducts and reactants, and B is the magnetic induction in gauss. Forthe conversion of a diamagnetic species into a paramagnetic species,Δχ_(m)≦0.01 cm³/mole. In a 1 Tesla (T) (1 Tesla=10 kGauss) appliedfield, |ΔG_(m)|≦0.05 J/mole. Even in the strongest laboratory fields of10 T, the effect is negligible compared to typical free energies ofreaction (≅kJ/mole). These are macroscopic arguments for systems wherethe magnet is placed external to the cell and a uniform field is appliedto the solution. Microscopically, it may be possible to argue that localfields in composites are substantial, and molecules in composites withina short distance of the source of the magnetic field experience stronglocal fields. For example, for a magnetic wire or cylinder, the magneticfield falls off over a distance, x, as x⁻³. The field experienced by amolecule 1 nm from the magnet is roughly 10²¹ times larger than thefield experienced at 1 cm. This argument is crude, but qualitativelyillustrates the potential advantage of a microstructural magneticcomposite. (As an example, in the magnetic/Nafion (DuPont) composites, alarger fraction of the redox species are probably transported throughthe 1.5 nm zone at the interface between the Nafion and the magneticparticles.) These redox species must therefore experience large magneticfields in close proximity to the interface.

Kinetics

Reaction rates, k, are parameterized by a pre-exponential factor, A, anda free energy of activation, ΔG^(‡); k=A exp[−ΔG^(‡)/RT]. An externallyapplied, homogeneous magnetic field will have little effect on ΔG^(‡),but can alter A. Nonadiabatic systems are susceptible to field effects.Magnetic fields alter the rate of free radical singlet-tripletinterconversions by lifting the degeneracy of triplet states (affectingΔG^(‡)); rates can be altered by a factor of three in simple solvents.Because magnetic coupling occurs through both electronic nuclearhyperfine interactions and spin-orbit interactions, rates can benonmonotonic functions of the applied field strength. Photochemical andelectrochemical luminescent rates can be altered by applied fields. Forsinglet-triplet interconversions, magnetic fields alter productdistributions when they cause the rate of interconversion to becomparable to the rate at which free radicals escape solvent cages.These effects are largest in highly viscous media, such as polymer filmsand micellar environments. Larger effects should be observed as thedimensionality of the system decreases. For coordination complexes,photochemical and homogeneous electron transfer rates are altered bymagnetic fields. Spin-orbit coupling is higher in transition metalcomplexes than organic radicals because of higher nuclear charge andpartially unquenched orbital angular momentum of the d- or f-shellelectrons. The rate of homogeneous electron transfer between Co(NH₃)₆ ³⁺and Ru(NH₃)₆ ²⁺ is below that expected for diffusion controlledreactions; in a 7 T magnetic field, the rate is suppressed two tothree-fold. It has been argued that Δχ_(m) (and ΔG_(m)) is set by themagnetic susceptibility of the products, reactants, and activatedcomplex, and a highly paramagnetic activated complex accounts for thefield effect. For reversible electron transfer at electrodes in magneticfields, no significant effect is expected. For quasireversible electrontransfer with paramagnetic and diamagnetic species, electron transferrates and transfer coefficients (α) are unchanged by magnetic fieldsapplied parallel to electrodes. Magnetic fields applied perpendicular toelectrodes in flow cells generate potential differences, which justsuperimpose on the applied electrode potentials. Potentials of 0.25Vhave been reported. Reversing the applied magnetic field reverses thesign of the potential difference. This effect does not change standardrate constants, only the applied potential.

Mass Transport

Magnetically driven mass transport effects have been studied inelectrochemical cells placed between the poles of large magnets. Effectsvary depending on the orientation of the electrode, the relativeorientation of the magnetic field and the electrode, forced or naturalconvection, and the relative concentrations of the redox species andelectrolyte. Three cases are illustrated in FIGS. 1, 2 and 3.

For a charged species moving by natural or forced convection parallel toan electrode and perpendicular to a magnetic field which is alsoparallel to the electrode, a Lorentz force is generated which moves thecharged particle toward the electrode (FIG. 1). This magnetohydrodynamiceffect is characterized by

F=q(E+v×B)  (1)

where F, E, v, and B are vectors representing the Lorentz force on thecharged species, the electric field, the velocity of the moving species,and the magnetic field, respectively; and q is the charge on thespecies. For flow cells and vertical electrodes, flux enhancements of afew-fold and reductions in the overpotential of a few tenths volts havebeen found in the presence of the magnetic field. Also, embedded inEquation 1 is the Hall effect; when a charged species moves through aperpendicular magnetic field, a potential is generated. This potentialsuperimposes on the applied potential and causes migration in lowelectrolyte concentrations.

When the electrode and magnetic field are parallel to the earth, thermalmotion leads to vortical motion at the electrode surface unless thefield (B) and the current density (j) are spatially invariant andmutually perpendicular (see FIG. 2). This is parameterized as:

F _(v) =c ⁻¹ [j×B]  (2)

In Equation (2) F_(v) is the vector of magnetic force per volume and cis the speed of light. In general, these forces are smaller than Lorentzforces; flux enhancements of a few-fold and potential shifts of 10 to 20mV are observed. Flux enhancements of paramagnetic and diamagneticspecies are similar, but paramagnetic electrolytes enhance the flux ofdiamagnetic Zn²⁺ two-fold. Vortices suppress thermal motion and eddydiffusion.

The final configuration, shown in FIG. 3, is for the magnetic fieldperpendicular to the electrode surface, and, therefore, parallel to theelectric field. Various, and sometimes inconsistent, results arereported for several configurations: for vertical electrodes inquiescent solution, flux enhancements of ≦1000%; for electrodes parallelto the earth with forced convection, flux retardations of 10%; and forelectrodes parallel to the earth and no forced convection, bothenhancements and no enhancements are reported.

The above summarizes the thermodynamic, kinetic, and mass transporteffects for systems where the magnetic field is applied uniformly acrossa cell with an external magnet. None of these macroscopic effectspredict or address properties dependent on the magnetic susceptibilityof the redox species. Quantum mechanical effects may also be important,especially on short length scales.

Fuel Cells

Since the incomplete reduction of oxygen limits the efficiency of H₂/O₂solid polymer electrolyte fuel cells, the cathode must be pressurizedabout five-fold over the anode.

Proton exchange membrane (PEM) fuel cell design is one which employshydrogen as an anode feed and oxygen in air as a cathode feed. Thesefuels are decomposed electrolytically (to yield water) at electrodestypically modified with a noble metal catalyst. The hydrogen and oxygenare separated from each other by a proton exchange membrane (such asNafion) to prevent thermal decomposition of the fuels at the noble metalcatalyst. The reactions at the cathode can be summarized as follows:Cathode  O₂ + 4H⁺ + 4e = 2H₂O  E^(∘)_(cathode) = 1.23V$\begin{matrix}{Anode} \\{{Net}\quad {Reaction}}\end{matrix}\quad \frac{{{2H^{+}} + {2e}} = H_{2}}{{O_{2} + {2H_{2}}} = {2H_{2}O}}\quad \frac{{E{^\circ}}_{anode} = {0.00V}}{{E{^\circ}}_{cell} = {1.23V}}$

However, the fuel cell is typically run under non-equilibriumconditions, and, as such, is subject to kinetic limitations. Theselimitations are usually associated with the reaction at the cathode.

O₂+4H⁺+4e=2H₂O E°_(cathode)=1.23V

As the reaction at the cathode becomes increasingly kinetically limited,the cell voltage drops, and a second reaction path, the two electron/twoproton reduction of oxygen to peroxide, becomes increasingly favored.This consumes oxygen in two electron steps with lower thermodynamicpotential.

O₂+2H⁺+2e=H₂O₂ E°H₂O₂=0.68V

The standard free energy of this reaction is 30% of the free energyavailable from the four electron reduction of oxygen to water. Thedecrease in current associated with the decreased number of electronstransferred and the decreased cell potential couple to yieldsubstantially lower fuel cell power output.

One approach to enhance the efficiency of the cathodic reaction is toincrease the concentration (pressure) of the feeds to thecathode—protons and oxygen—so as to enhance the flux (i.e., the reactionrate at the cathode in moles/cm²s⁻¹) at the cathode. The proton flux isreadily maintained at a sufficiently high value by the proton exchangemembrane (usually Nafion) so as to meet the demand set by the cathodereaction. Normally, the method of enhancing the flux and biasing thereaction to favor the formation of water is to pressurize the air feedto the cathode. Pressures of 5-10 atmospheres are typical.

The need to pressurize air to the cathode in PEM fuel cells has been amajor obstacle in the development of a cost effective fuel cell as areplacement for the internal combustion engine, e.g. in a vehicle. Inparticular, pressurization of the cathode requires compressors. Intransportation applications, power from the fuel cell is needed to runthe compressor. This results in approximately 15% reduction in the poweroutput of the total fuel cell system.

By developing a passive pressurization method for a fuel cell, themechanical pumps could be eliminated from the fuel cell system. This hasnumerous advantages. The weight of a fuel cell would be decreased almost40% by eliminating mechanical pumps. With the elimination of theparasitic loss of running the pumps, and improving cathode performance,the fuel cells would provide a higher energy and power density. Anypotential shift at the electrode surface driven by the magneticcomponents can be exploited to enhance the voltage output of the fuelcell, and to overcome the poor kinetics of the cathode. Eliminating thepumps also eliminates the only moving parts of the fuel cell, andthereby, the likelihood of fuel cell failure is drastically reduced.

In current fuel cell design, the cathode is pressurized to approximatelyfive times the pressure of the anode. This pressurization constrains thedesign of the fuel cell to be sufficiently rigid as to support thispressure. In a magnetically based, passive pressurization scheme, theneed for the rigid structure is eliminated. This has two majoradvantages. First, the weight and bulk of the fuel cell is decreased.Second, the fuel cell is now a flexible device. The flexibility can beexploited in various ways, including placing fuel cells into unusualgeometries and structures, thereby exploiting space in structures anddevices which might otherwise be lost. Also, the flexible nature of thefuel cell allows a single structure to be divided readily into severalsmaller cells, which can be connected into different parallel and serialconfigurations to provide variable voltage and current outputs. Such adivision is more complicated in the more rigid structures of apressurized fuel cell because the encasing walls limit access to thefuel cell electrodes.

Electrode Passivation

At present, many fuel cell designs are focused on hydrogen as fuel, duein part to the favorable kinetics for hydrogen at the anode. However,hydrogen has the disadvantage of being difficult and somewhat dangerousto store. This disadvantage is particularly apparent in portable fuelcell applications (e.g. vehicular and portable device applications, suchas lap-top computers). For vehicular fuel cell applications a liquidfuel, such as methanol, is generally preferred. In prior art fuel cellsemploying methanol as fuel, methanol is reformed thermally over a copperzinc or other catalyst to form hydrogen (and carbon dioxide), which isfed to the anode on demand.

Direct reformation of liquid fuels (e.g. methanol, ethanol) at theanode, although much preferred, is not efficient using prior art fuelcells. This is so because, in prior art fuel cells, a passivating layerrapidly forms on the surface of the anode due to reaction of the anodesurface with intermediates of the electrolysis, i.e., the electrode isrendered passive, and as a result further reaction stops or issignificantly impeded.

Despite extensive investigations over the past several decades, littleprogress has been made in developing direct reformation of a fuel at theelectrode(s) of a fuel cell. This is particularly true in the case ofdirect reformation at ambient temperatures. This lack of progress is adirect consequence of the lack of resolution of the problem of electrodepassivation. To date, almost all efforts to resolve this problem havefocused on chemical techniques and methods, as opposed to thephysical/magnetic approach adopted under the present invention.

Data presented below demonstrate that electrodes modified with amagnetic composite are either not passivated or passivated less thanunmodified electrodes, i.e. such modified electrodes resist passivation;whereas unmodified electrodes are rapidly passivated, during oxidationof a liquid fuel. According to the present invention, the directreformation of liquid fuel in fuel cell applications is possible. Thepresent invention may also be broadly applicable to the prevention ofpassivation in the case of all electrolyses which proceed via either afree radical mechanism, or a multi-electron transfer process.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an improvedelectrode.

Another object of the invention is to provide a coating on an electrodeto enhance the flux of magnetic species to the electrode.

Another object of the invention is to provide a separator to separatemagnetic species from each other dependent upon magnetic susceptibility.

Another object of the invention is to provide a method for making acoating for an electrode to improve the flux of magnetic species to theelectrode.

Another object of the invention is to provide a method for coating asurface of a device with a magnetic composite material responsive to anexternal magnetic field.

Another object of the invention is to provide a method for coating asurface of a device with a magnetic composite material having aplurality of boundary regions with magnetic gradients having paths tothe coated surface when an external magnetic field is applied to thecoated surface.

Another object of the invention is to provide an improved fuel cell.

Another object of the invention is to provide an improved cathode in afuel cell.

Another object of the invention is to provide an improved battery.

Another object of the invention is to provide an improved membranesensor.

Another object of the invention is to provide an improved flux switch.

Another object of the invention is to provide an improved fuel cellcathode with passive oxygen pressurization.

Another object of the invention is to provide an improved separator forseparating paramagnetic species from diamagnetic species.

Another object of the invention is to provide an improved electrolyticcell.

Another object of the invention is to provide an improved electrolyticcell for an electrolyzable gas.

Another object of the invention is to provide an improved graded densitycomposite for controlling chemical species transport.

Another object of the invention is to provide an improved dual sensor.

Another object of the invention is to provide an improved electrode fordirect reformation of liquid or gaseous fuels.

Another object of the invention is to provide an improved electrodewhich does not passivate or which resists formation of a passivatinglayer on the electrode surface.

Another object of the invention is to provide an electrochemical cellhaving improved power generation and/or synthetic capability.

Another object of the invention is to provide an electrochemical cellhaving an electrode which is not passivated by electrolysisintermediates.

Another object of the invention is to provide an improved fuel cellhaving an electrode which resists passivation by electrolysisintermediates and which permits the direct reformation of a liquid orgaseous fuel.

Another object of the invention is to provide a magnetic compositematerial or composition for coating the surface of an electrode, whereinthe electrode does not passivate or form a passivating layer on theelectrode surface.

Another object of the invention is to provide a method for coating thesurface of an electrode, wherein the electrode does not passivate orform a passivating layer on the electrode surface.

Another object of the invention is to provide a method for coating thesurface of an electrode, wherein the electrode allows direct reformationof a liquid or gaseous fuel.

Another object of the invention is to provide a method for preventing anelectrode from forming a passivating layer on the electrode surface.

Another object of the invention is to provide a method which enablesdirect reformation of a liquid or gaseous fuel at the electrode surfaceof a fuel cell.

Another object of the invention is to provide a method for directreformation of a liquid or gaseous fuel at the surface of an electrodewherein the surface of the electrode is not passivated.

One advantage of the invention is that it can enhance the flux ofparamagnetic species to an electrode.

Another advantage of the invention is that it can enhance the flux ofoxygen to the cathode in a fuel cell, equivalent to passivepressurization.

Another advantage of the invention is that it can separate paramagnetic,diamagnetic, and nonmagnetic chemical species from a mixture.

Another advantage of the invention is that it can separate chemicalspecies according to chemical, viscosity, and magnetic properties.

Another advantage of the invention is that it can take advantage ofmagnetic field gradients in magnetic composites.

Another advantage of the invention is that it can be designed to workwith internal or external magnetic fields, or both.

Another advantage of the invention is that it avoids the formation of apassivating layer on the surface of an electrode.

Another advantage of the invention is that it permits the directreformation of a liquid or gaseous fluid at the surface of a fuel cellelectrode.

Another advantage of the invention is that it establishes magneticfields at the surface of an electrode.

Another advantage of the invention is that it stabilizes free radicalsgenerated during the electrolysis process.

One feature of the invention is that it includes a magnetically modifiedelectrode.

Another feature of the invention is that it includes a process forcoating a surface of a device with a magnetic composite materialresponsive to an external magnetic field, wherein the coating impartsincreased electrochemical efficiency, and or increased flux, at saidsurface.

Another feature of the invention is that it includes magnetic compositesmade from ion exchange polymers and non-permanent magnet microbeads withmagnetic properties which are susceptible to externally applied magneticfields.

Another feature of the invention is that it includes magnetic compositesmade from ion exchange polymers and organo-Fe (superparamagnetic orferrofluid) or other permanent magnetic and nonpermanent magnetic orferromagnetic or ferrimagnetic material microbeads which exhibitmagnetic field gradients.

Another feature of the invention is that it includes magnetic compositescomprising particles containing platinum, wherein the platinum serves asa catalyst and/or an electron conductor.

Another feature of the invention is that it includes an improvedelectrode having a magnetic composite disposed thereon, wherein theelectrode is not passivated by intermediates of electrolysis.

Another feature of the invention is that it includes a magneticcomposite composition for coating a surface of an electrode, wherein theformation of a passivating layer at the surface of the electrode isavoided.

Another feature of the invention is that it includes a magneticcomposite composition for coating the surface of an electrode which doesnot passivate or form a passivating layer on the electrode surface andpermits the direct reformation of fuels by the electrode.

Another feature of the invention is that it includes magneticcomposites, comprising carbon particles associated with a catalyst, incombination with an ion exchange polymer, and magnetic microbeads, whichenable the direct reformation of liquid or gaseous fuels at the surfaceof a fuel cell electrode, without the formation of a passivating layerat the surface of the electrode.

Another feature of the invention is that it includes magneticcomposites, comprising carbon particles associated with a catalyst, incombination with an ion exchange polymer, and magnetic microbeads, whichenable the stabilization of free radicals generated during theelectrolysis process, wherein the formation of a passivating layer atthe surface of the electrode is avoided.

Another feature of the invention is that it includes an electrochemicalcell having at least one electrode with a magnetic composite materialdisposed on the surface thereof, wherein the electrochemical cellprovides enhanced power generation and/or synthetic capability.

These and other objects, advantages and features are accomplished by aseparator arranged between a first region containing a first type ofparticle and a second type of particle and a second region, comprising:a first material having a first magnetism; a second material having asecond magnetism; a plurality of boundaries providing a path between thefirst region and the second region, each of the plurality of boundarieshaving a magnetic gradient within the path, the path having an averagewidth of approximately one nanometer (nm) to approximately severalmicrometers (μm), wherein the first type of particles have a firstmagnetic susceptibility and the second type of particles have a secondmagnetic susceptibility, wherein the first and the second magneticsusceptibilities are sufficiently different that the first type ofparticles pass into the second region while most of the second type ofparticles remain in the first region.

These and other objects, advantages and features are also accomplishedby the provision of a cell, comprising: an electrolyte including a firsttype of particles; a first electrode arranged in the electrolyte; and asecond electrode arranged in the electrolyte wherein the first type ofparticles transform into a second type of particles once the first typeof particles reach the second electrode, the second electrode having asurface with a coating which includes: a first material having a firstmagnetism; a second material having a second magnetism; a plurality ofboundaries providing a path between the electrolyte and the surface ofthe second electrode, each of the plurality of boundaries having amagnetic gradient within the path, the path having an average width ofapproximately one nanometer to approximately several micrometers,wherein the first type of particles have a first magnetic susceptibilityand the second type of particles have a second magnetic susceptibility,and the first and the second magnetic susceptibilities are different.

These and other objects, advantages and features are also accomplishedby the provision of a method of coating a surface with a magneticcomposite material, comprising the steps of: preparing a casting mixturecomprising magnetic microbeads and an ion exchange polymer; casting thecasting mixture on the surface; and drying the casting mixture to yielda magnetic composite coating on the surface.

These and other objects, advantages and features are also accomplishedby the provision of a method of coating a surface of a device with amagnetic composite material, comprising the steps of: mixing a firstcomponent comprising at least about 1% by weight of magnetic microbeadsin a first solvent with a second component comprising at least about 2%by weight of an ion exchange polymer in a second solvent to yield amixed suspension or casting mixture; applying the mixed suspension tothe surface, the surface being arranged in an external magnetic field ofat least about 0.5 Tesla and being oriented approximately 90° withrespect to the normal of the electrode surface; and evaporating thefirst solvent and the second solvent to yield a surface coating having aplurality of boundary regions with magnetic gradients having paths tothe coated surface.

These and other objects, advantages and features are also accomplishedby the provision of a method of making an electrode with a surfacecoated with a magnetic composite with a plurality of boundary regionswith magnetic gradients having paths to the surface of the electrode,comprising the steps of: mixing a first component which includes asuspension of at least approximately 1 percent by weight of inertpolymer coated magnetic microbeads containing between approximately 10percent and approximately 90 percent magnetizable material havingdiameters at least 0.5 μm in a first solvent with a second component ofat least approximately 2 percent by weight of an ion exchange polymer ina second solvent to yield a mixed suspension; applying the mixedsuspension to the surface of the electrode, the electrode being arrangedin a magnetic field of at least approximately 0.05 Tesla and beingoriented approximately 90 degrees with respect to the normal of theelectrode surface; and evaporating the first solvent and the secondsolvent to yield the electrode with a surface coated with the magneticcomposite having a plurality of boundary regions with magnetic gradientshaving paths to the surface of the electrode.

These and other objects, advantages and features are furtheraccomplished by a method of making an electrode with a surface coatedwith a composite with a plurality of boundary regions with magneticgradients having paths to the surface of the electrode when an externalmagnetic field is turned on, comprising the steps of: mixing a firstcomponent which includes a suspension of at least 5 percent by weight ofinert polymer coated microbeads containing between 10 percent and 90percent magnetizable non-permanent magnetic material having diameters atleast 0.5 μm in a first solvent with a second component comprising atleast 5 percent by weight of an ion exchange polymer in a second solventto yield a casting mixture or mixed suspension; applying the mixedsuspension to the surface of the electrode; evaporating the firstsolvent and the second solvent to yield the electrode with a surfacecoated with the composite having a plurality of boundary regions withmagnetic gradients having paths to the surface of the electrode when anexternal magnet is turned on.

These and other objects, advantages and features are also accomplishedby a method of forming a graded density layer, comprising the steps of:formulating a series of casting mixtures, each of the series of castingmixtures comprising a polymeric material and a solvent, wherein theseries of casting mixtures have a range of concentrations of thepolymeric material; applying to a surface a film of one of the series ofcasting mixtures and evaporating the solvent; and, further applying tothe surface a film of another of the series of casting mixtures andevaporating the solvent, to yield a coating of the graded density layeron the surface.

These and other objects, advantages and features are also accomplishedby an electrode for channeling flux of magnetic species comprising: aconductor; a composite of a first material having a first magnetism anda second material having a second magnetism in surface contact with theconductor, wherein the composite comprises a plurality of boundariesproviding pathways between the first material and the second material,wherein the pathways channel the flux of the magnetic species throughthe pathways to the conductor.

These and other objects, advantages and features are furtheraccomplished by an electrode for effecting electrolysis of magneticspecies comprising: a conductor; and magnetic means in surface contactwith the conductor for enhancing the flux of the magnetic species in anelectrolyte solution to the conductor and thereby effecting electrolysisof the magnetic species.

These and other objects, advantages and features are furtheraccomplished by an electrode for effecting electrolysis of magneticspecies comprising: a conductor; and means in surface contact with theconductor for enhancing the flux of the magnetic species to theconductor and thereby effecting electrolysis of the magnetic species.

These and other objects, advantages and features are yet furtheraccomplished by an electrode for electrolysis of magnetic speciescomprising: a conductor; a composite magnetic material in surfacecontact with the conductor, the composite magnetic material having aplurality of transport pathways through the composite magnetic materialto enhance the passage of the magnetic species to the conductor andthereby effecting electrolysis of the magnetic species.

These and other objects, advantages and features are also accomplishedby a system, comprising: a first electrolyte species with a firstmagnetic susceptibility; a second electrolyte species with a secondmagnetic susceptibility; and a means for channeling the firstelectrolyte species with a first magnetic susceptibility preferentiallyover the second electrolyte species with a second magneticsusceptibility, wherein the means comprises a first material having afirst magnetism forming a composite with a second material having asecond magnetism.

These and other objects, advantages and features are also accomplishedby a system for separating first particles and second particles withdifferent magnetic susceptibilities comprising: a first magneticmaterial with a first magnetism; and a second magnetic material with asecond magnetism working in conjunction with the first magnetic materialto produce magnetic gradients, wherein the magnetic gradients separatethe first particles from the second particles.

These and other objects, advantages and features are accomplished by acomposite material for controlling chemical species transportcomprising: an ion exchanger; and a graded density layer, wherein theion exchanger is sorbed into the graded density layer.

These and other objects, advantages and features are furtheraccomplished by a magnetic composite material for controlling magneticchemical species transport according to magnetic susceptibilitycomprising: an ion exchanger; a polymer coated magnetic microbeadmaterial; and a graded density layer, wherein the ion exchanger and thepolymer coated magnetic microbead material are sorbed into the gradeddensity layer.

These and other objects, advantages and features are furtheraccomplished by a composite material for controlling chemical speciesviscous transport comprising: an ion exchanger; a graded viscositylayer, wherein the ion exchanger is sorbed into the graded viscositylayer.

These and other objects, advantages and features are furtheraccomplished by a magnetic composite material for controlling magneticchemical species transport and distribution comprising: an ionexchanger; a polymer coated magnetic microbead material; and a gradeddensity layer, wherein the ion exchanger and the polymer coated magneticmicrobead material are sorbed into the graded density layer forming agradient in the density of the polymer coated magnetic microbeadmaterial substantially perpendicular to a density gradient in the gradeddensity layer.

These and other objects, advantages and features are furtheraccomplished by a magnetic composite material for controlling magneticchemical species transport and distribution comprising: an ionexchanger; a polymer coated magnetic microbead material; and a gradeddensity layer, wherein the ion exchanger and the polymer coated magneticmicrobead material are sorbed into the graded density layer forming agradient in the density of the polymer coated magnetic microbeadmaterial substantially parallel to a density gradient in the gradeddensity layer.

These and other objects, advantages and features are also accomplishedby an ion exchange composite with graded transport and chemicalproperties controlling chemical species transport comprising: an ionexchanger; and a staircase-like graded density layer having a first sideand a second side, wherein the ion exchanger is one of sorbed into thegraded density layer and cocast on the graded density layer and thestaircase-like graded density layer and the ion exchanger are containedwithin the first side and the second side, wherein the first side is incloser proximity to the source of the chemical species and the secondside is more distal to the source of the chemical species, and whereinthe staircase-like graded density layer has lower density toward thefirst side and higher density toward the second side, substantiallyincreasing in density in a direction from the first side toward thesecond side.

These and other objects, advantages and features are also accomplishedby an ion exchange composite with graded transport and chemicalproperties controlling chemical species transport comprising: an ionexchanger; and a staircase-like graded density layer having a first sideand a second side, wherein the ion exchanger is one of sorbed into thegraded density layer and cocast on the graded density layer, and the ionexchanger and the stair case-like graded density layer are containedwithin the first side and the second side, wherein the first side is incloser proximity to the source of the chemical species and the secondside is more distal to the source of the chemical species, and whereinthe staircase-like graded density layer has higher density toward thefirst side and lower density toward the second side, substantiallydecreasing in density in a direction from the first side toward thesecond side.

These and other objects, advantages and features are accomplished alsoby a dual sensor for distinguishing between a paramagnetic species and adiamagnetic species comprising: a magnetically modified membrane sensor;and an unmodified membrane sensor, wherein the magnetically modifiedmembrane sensor preferentially enhances the concentration of and allowsthe detection of the paramagnetic species over the diamagnetic speciesand the unmodified membrane sensor enhances the concentration of andallows the detection of the diamagnetic species and the paramagneticspecies, enabling the measurement of the concentration of at least theparamagnetic species.

These and other objects, advantages and features are furtheraccomplished by a dual sensor for distinguishing between a paramagneticspecies and a nonmagnetic species comprising: a magnetically modifiedmembrane sensor; an unmodified membrane sensor, wherein the magneticallymodified membrane sensor preferentially enhances the concentration ofand allows the detection of the paramagnetic species over thenonmagnetic species and the unmodified membrane sensor enhances theconcentration of and allows the detection of the nonmagnetic species andthe paramagnetic species, enabling the measurement of the concentrationof at least the paramagnetic species.

These and other objects, advantages and features are furtheraccomplished by a dual sensor for distinguishing between a firstdiamagnetic species and a second diamagnetic species comprising: amagnetically modified membrane sensor; and a differently magneticallymodified membrane sensor; wherein the magnetically modified membranesensor preferentially enhances the concentration of and allows thedetection of the first diamagnetic species over the second diamagneticspecies and the differently magnetically modified membrane sensorenhances the concentration of and allows the detection of the secondparamagnetic species and the diamagnetic species, enabling themeasurement of the concentration of at least the first diamagneticspecies.

These and other objects, advantages and features are furtheraccomplished by a dual sensor for distinguishing between a firstparamagnetic species and a second paramagnetic species comprising: amagnetically modified membrane sensor; and a differently magneticallymodified membrane sensor, wherein the magnetically modified membranesensor preferentially enhances the concentration of and allows thedetection of the first paramagnetic species over the second paramagneticspecies and the differently magnetically modified membrane sensorenhances the concentration of and allows the detection of the secondparamagnetic species and the first paramagnetic species, enabling themeasurement of the concentration of at least the first paramagneticspecies.

These and other objects, advantages and features are furtheraccomplished by a dual sensor for distinguishing between a diamagneticspecies and a nonmagnetic species comprising: a magnetically modifiedmembrane sensor; and an unmodified membrane sensor, wherein themagnetically modified membrane sensor preferentially enhances theconcentration of and allows the detection of the diamagnetic speciesover the nonmagnetic species and the unmodified membrane sensor enhancesthe concentration of and allows the detection of the nonmagnetic speciesand the diamagnetic species, enabling the measurement of theconcentration of at least the diamagnetic species.

These and other objects, advantages and features are furtheraccomplished by a flux switch to regulate the flow of a redox speciescomprising: an electrode; a coating on the electrode, wherein thecoating is formed from a composite comprising: a magnetic microbeadmaterial with aligned surface magnetic field; an ion exchange polymer;and an electro-active polymer in which a first redox form isparamagnetic and a second redox form is diamagnetic, wherein the fluxswitch is actuated by electrolyzing the electro-active polymer from thefirst redox form ordered in the magnetic field established by thecoating to the second redox form disordered in the magnetic field.

These and other objects, advantages and features are also accomplishedby a flux switch to regulate the flow of a chemical species comprising:an electrode; and a coating on the electrode, wherein the coating isformed from a composite comprising: a non-permanent magnetic microbeadmaterial; an ion exchange polymer; and a polymer with magnetic materialcontained therein in which a first form is paramagnetic and a secondform is diamagnetic, wherein the flux switch is actuated by reversiblyconverting from the paramagnetic form to the diamagnetic form when anexternally applied magnetic field is turned on or off.

These and other objects, advantages and features are furtheraccomplished by a magnetic composite comprising particles containingplatinum, wherein the platinum serves as a catalyst and/or an electronconductor.

These and other objects, advantages and features are furtheraccomplished by a magnetic composite material or composition forpreventing or impeding electrode passivation, comprising: an ionexchange polymer; magnetic microbeads; and carbon particles inassociation with a catalyst, wherein the magnetic composite material isdisposed on the surface of the electrode and prevents passivation of theelectrode surface.

These and other objects, advantages and features are furtheraccomplished by a magnetic composite material disposed on the surface ofan electrode for preventing electrode passivation and enabling directreformation of a fuel at the surface of a fuel cell electrode,comprising: an ion exchange polymer; magnetic microbeads; and/or carbonparticles in association with a catalyst, wherein the magnetic compositematerial prevents passivation of the electrode surface and enablesdirect reformation of the fuel at the electrode surface.

These and other objects, advantages and features are also accomplishedby the provision of a method of making an electrode with a surfacecoated with a magnetic composite, comprising the steps of: forming acasting mixture comprising an ion exchange polymer, magnetic microbeads,and/or carbon particles in association with a catalyst, and at least onesolvent; casting the casting mixture on the surface of the electrode;and evaporating the solvent, to yield an electrode having a surfacecoated with the magnetic composite, wherein the magnetic compositeprevents passivation of the electrode surface.

These and other objects, advantages and features are also accomplishedby the provision of a method of making an electrode with a surfacecoated with a magnetic composite, comprising the steps of: forming acasting mixture comprising an ion exchange polymer, magnetic microbeads,carbon particles in association with a catalyst, and at least onesolvent; casting the casting mixture on the surface of the electrode;before the solvent evaporates, arranging the electrode in an externalmagnetic field to orient the magnetic particles and form an orderedstructure on the surface of the electrode; and evaporating the solvent,to yield an electrode having a surface coated with the magneticcomposite, wherein the magnetic composite prevents passivation of theelectrode surface.

These and other objects, advantages and features are also accomplishedby the provision of a method for direct reformation of a liquid orgaseous fuel at the surface of a magnetically modified electrode of afuel cell, comprising the step of: delivering the fuel directly to thesurface of the electrode, the surface of the electrode having a magneticcomposite coating disposed thereon which prevents passivation of thesurface of the electrode and enables direct reformation of the fuel atthe surface of the magnetically modified electrode.

These and other objects, advantages and features are also accomplishedby the provision of a fuel cell, comprising: at least one electrodehaving a magnetic composite disposed on the surface of the at least oneelectrode; and delivering means for delivering a fluid (liquid orgaseous) fuel to the at least one surface of the electrode, wherein thefuel is oxidized (reformed) directly at the at least one anode, and themagnetic composite prevents passivation of the at least one electrode.

These and other objects, advantages and features are also accomplishedby the provision of a fuel cell, comprising: an anode having a magneticcomposite disposed on the surface of the anode; and delivering means fordelivering fuel to the surface of the anode, wherein the fuel isreformed directly at the anode, and the magnetic composite preventspassivation of the anode surface.

The above and other objects, advantages and features of the inventionwill become more apparent from the following description thereof takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the influence of electrode orientation and solvent motionon magnetohydrodynamic fluid motion for one geometry.

FIG. 2 shows the influence of electrode orientation and solvent motionon magnetohydrodynamic fluid motion for a second geometry.

FIG. 3 shows the influence of electrode orientation and solvent motionon magnetohydrodynamic fluid motion for a third geometry.

FIGS. 4A and 4B show plots of km values for neutron-track etchedpolycarbonate/Nafion composites versus functions of pore diameter, d.

FIGS. 5A and 5B show the surface diffusion model assuming no limitationsto the transport rate in the radial direction.

FIGS. 6A and 6B show the surface diffusion model including radialmigration.

FIGS. 7A and 7B show κm values of hydroquinone throughpolystyrene/Nafion composites for ratios of surface area of themicrobeads to volume of Nafion.

FIG. 8A shows an analysis of fractal diffusion along the surface of themicrobeads in polystyrene Microbead/Nafion composites.

FIG. 8B shows flux measurements by cyclic voltammetry for two electrodesbearing surface modifications of Nafion plus 15% by volume of non-coatedparticles of iron(III) oxide, or Nafion alone. Voltammogram 1 is for theelectrode bearing a simple film of Nafion coated on the surface of theelectrode. Voltammogram 2 is for an electrode bearing the compositecomprising Nafion and 15% non-coated particles of iron(III) oxide.

FIG. 9 shows the relative flux of redox species on the y-axis, where themaximum cyclic voltammetric current for a composite with magneticmicrobeads is normalized by the maximum cyclic voltammetric current fora Nafion film containing no magnetic material, with the ratio giving theflux enhancement.

FIG. 10 shows κm values for Ru(NH₃)₆ ³⁺ as a function of volume fractionof microbeads in magnetic and nonmagnetic composites.

FIG. 11 shows flux increases with magnetic content of microbeads forRu(NH₃)₆ ³⁺.

FIGS. 12A, 12B, and 12C show cyclic voltammetric results for thereversible species Ru(NH₃)₆ ³⁺ and Ru(bpy)₃ ²⁺ and for thequasireversible species hydroquinone.

FIG. 13 shows a plot of the flux for seven redox species that is usedfor predicting a roughly five-fold flux enhancement of oxygen through a15% magnetic Nafion composite over Nafion.

FIG. 14 shows a plot of the flux of Ru(NH₃)₆ ³⁺ in magnetic bead/Nafioncomposites increasing as the fraction of magnetic beads increases.

FIG. 14A shows a plot of the paramagnetic effective moments oflanthanide metals and compounds as a function of the number of f-shellelectrons.

FIG. 14B shows a plot of the paramagnetic effective moments of actinidemetals and compounds as a function of the number of f-shell electrons.

FIG. 14C shows a plot of the magnetic moments of d-shell transitionmetals as a function of the number of d-shell electrons.

FIG. 14D shows a series of vats separated by magnetic separators used toseparate mixtures to increase constituent purity according to theinstant invention.

FIG. 15A shows a simplified representation used to describe how magneticmicroboundaries influence a standard electrochemical process.

FIG. 15B shows a simplified representation of embodiments of theinvention placed in an externally applied magnetic field provided by anelectromagnet to alter the magnetic properties of those embodiments,where the field may be turned on or off, or it may be oscillated.

FIG. 16 shows a simplified diagram of a separator with no electrode orconductive substrate which separates a mixture of particles between afirst solution and a second solution.

FIG. 16A shows a series of vats separated by magnetic separators used toseparate mixtures to increase constituent purity similar to FIG. 14D,but which uses a ligand to form complexes that aid in the separationaccording to the present invention.

FIG. 16B shows a series of vats separated by magnetic separators used toseparate mixtures to increase constituent purity similar to FIG. 14D,but which uses a ligand associated with the magnetic separators to formcomplexes that aid in the separation according to the present invention.

FIG. 16C shows a series of vats separated by magnetic separators used toseparate mixtures that combines separation similar to FIG. 14D withseparation using a ligand to form complexes that aid in the separationaccording to the present invention.

FIG. 16D shows two vats separated by a magnetic separator used toseparate mixtures that combines separation similar to FIG. 14D withseparation using a ligand to form complexes that aid in the separationalong with particle precipitation.

FIGS. 16E1-16E3 show fuel cells 1220 in arrangements.

FIG. 17 is a short summary of steps involved in a method of making anelectrode according to two embodiments of the invention.

FIGS. 18A and 18B show a flux switch 800 to regulate the flow of a redoxspecies according to yet another embodiment of the invention.

FIG. 19 shows a dual sensor 900 for distinguishing between a firstspecies (particles A) and a second species (particles B).

FIG. 20 shows a cell 201 according to another embodiment of theinvention. An embodiment of the chromatographic technique is shown inFIG. 20A.

FIG. 20B shows rough magnetic field lines in the iron wire.

FIG. 20C shows a method for the technique of FIG. 20A.

FIG. 21 shows cyclic voltammetric data for oxygen reduction using anelectrode having both magnetic microbeads and platinized carbonparticles incorporated into the electrode interface (curve No. 4), ascompared with corresponding data for three other electrode surfacemodifications (curve Nos. 1-3).

FIG. 22 shows a plot of kD^(1/2)C′ (y-axis) while the carbon masspercent (as platinized carbon) in the composite was varied over therange of 10% to 50%, where kD^(1/2)C′ is a parameter proportional to thepeak cyclic voltammetric current. The platinum content of carbon is 10,20, 30 or 40%. Each point represents a single experiment.

FIGS. 23A and 23B show cyclic voltammetric data for ethanol oxidation (6mM ethanol in 0.1 M Na₂SO₄) using a platinum electrode bearing a surfacecomposite comprising Nafion and either non-magnetic microbeads (FIG.23A) or magnetic microbeads (FIG. 23B) (25% beads, 75% Nafion, byvolume). Cyclic voltammograms were recorded at scan rates of 500, 200,100, 50, and 20 mV/s. The electrode was cycled 100 times between −700and 900 mV before the data was recorded.

FIGS. 24A, 24B, and 24C show cyclic voltammetric data for ethanoloxidation (7 mM ethanol in 0.1 M Na₂SO₄) using a platinum electrodebearing a surface composite comprising non-magnetic microbeads andNafion (25% beads, 75% Nafion, by volume), and using a platinumelectrode bearing a surface composite comprising magnetic microbeads andNafion (25% beads, 75% Nafion, by volume). Cyclic voltammograms wererecorded at a scan rate of 500 Mv/s (FIG. 24A), 100 mV/s (FIG. 24B), and20 mV/s (FIG. 24C). In each case, the electrode was cycled 100 timesbetween −700 and 900 mV before the data was recorded.

FIG. 25 shows cyclic voltammetric data for ethanol oxidation (6.852 mMethanol in 0.1003 M Na₂SO₄) using a bare platinum electrode. Cyclicvoltammograms were recorded at scan rates of 500, 200, 100, 50, and 20mV/s. The electrode was cycled 100 times between −700 and 900 mV beforethe data was recorded.

FIGS. 26A and 26B show cyclic voltammetric data for ethanol oxidation(6.852 mM ethanol in 0.1003 M Na₂SO₄) using a platinum electrode bearinga surface composite comprising platinized carbon (Pt—C), Nafion, andeither non-magnetic microbeads (FIG. 26A) or magnetic microbeads (FIG.26B), (11% beads, 26% Pt-C, and 75% Nafion, by volume). Cyclicvoltammograms were recorded at scan rates of 500, 200, 100, 50, and 20mV/s. The electrode was cycled 100 times between −700 and 900 mV beforethe data was recorded.

FIGS. 27A and 27B show cyclic voltammetric data for ethanol oxidation(6.852 mM ethanol in 0.1003 M Na₂SO₄) using a platinum electrode bearinga surface composite comprising Pt—C, Nafion, and either magneticmicrobeads (FIG. 27A) or non-magnetic microbeads (FIG. 27B), (11% beads,76% Pt—C, and 13% Nafion, by volume). Cyclic voltammograms were recordedat scan rates of 500, 200, 100, 50, and 20 mV/s. The electrode wascycled 100 times between −700 and 900 mV before the data was recorded.

FIG. 28A shows cyclic voltammetric data for ethanol oxidation (6 mMethanol in 0.1 M Na₂SO₄) using a bare platinum electrode, and usingplatinum electrodes bearing surface composites comprising Pt—C, Nafion,and either magnetic microbeads or non-magnetic microbeads, (11% beads,26% Pt—C, and 63% Nafion, by volume). Cyclic voltammograms were recordedat a scan rate of 500 mV/s. The electrode was cycled 100 times between−700 and 900 mV before the data was recorded.

FIG. 28B shows cyclic voltammetric data for ethanol oxidation, as forFIG. 28A, recorded at a scan rate of 100 mV/s.

FIG. 28C shows cyclic voltammetric data for ethanol oxidation, as forFIG. 28A, recorded at a scan rate of 20 mV/s.

FIG. 29A shows cyclic voltammetric data for ethanol oxidation (6 mMethanol in 0.1 M Na₂SO₄) using a bare platinum electrode, and usingplatinum electrodes bearing surface composites comprising Pt—C, Nafion,and either magnetic microbeads or non-magnetic microbeads, (11% beads,76% Pt—C, and 13% Nafion, by volume). Cyclic voltammograms were recordedat a scan rate of 500 mV/s. The electrode was cycled 100 times between−700 and 900 mV before the data was recorded.

FIG. 29B shows cyclic voltammetric data for ethanol oxidation, as forFIG. 29A, recorded at a scan rate of 100 mV/s.

FIG. 29C shows cyclic voltammetric data for ethanol oxidation, as forFIG. 29A, recorded at a scan rate of 20 mV/s.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Interfacial Gradients inGeneral

It has been found that interfacial gradients of concentration, charge,dielectric constant, and potential tend to establish strong, interfacialforces which decay over a microstructural distance (1 to 100 nm). (Forexample, for an applied potential of 10 mV to 100 mV past the potentialof zero charge at an electrode in 0.1 M aqueous electrolyte, theinterfacial potential gradient (¦electric field¦) is 10⁵ V/cm to 10⁶V/cm, but it decays over a distance of about 1 nm.) In a homogeneousmatrix, with few interfaces, interfacial gradients have a negligibleeffect on bulk material properties. However, in a microstructured matrixwhere the ratio of surface area to volume is high, interfacial gradientscan have a large effect on, or even dictate the properties of acomposite. Models appropriate to the description of bulk materials havebeen found to be unsatisfactory when applied to these composites.Moreover, such composites provide an opportunity to design matrices toperform functions and exhibit properties not found in homogeneousmaterials, as will be discussed.

The effects of gradients, associated with the interfaces between the ionexchanger and its support matrix, to enhance the transport of ions andmolecules have been studied in ion exchange polymer composites. Thecomposites were formed by sorbing ion exchange polymers into highsurface area substrates with well-established geometries. The flux ofsolutes through the composites was determined voltammetrically. When thesolute flux through the ion exchange portion of the composites and theflux through simple films of the ion exchanger were compared, fluxenhancements were observed for the composites. These enhancements wereoften greater than an order of magnitude. Consistently, the ratio ofsurface area of the substrate to the volume of sorbed ion exchanger(SA/Vol) has been the critical factor in quantifying the fluxenhancements. The flux enhancement characteristics were found to bedominated by the interface between the ion exchanger and the support.Several interfacial gradients have so far been identified as important:concentration gradients, leading to surface diffusion; electricpotential gradients, leading to migration; and magnetic field gradients,leading to flux enhancements and electric potential shifts atelectrodes.

Forming Composites

Composites were made by intimately mixing two or more components to forma heterogeneous matrix as will be discussed in more detail below. Whilecomposites retain some characteristics of their components, propertiesdistinct from those of the starting materials have been demonstratedthat make composites of special interest.

Results of Prior Studies

The impact of microstructure on transport and selectivity in ionexchange polymers and their composites has been found to be significant.Novel characteristics arose not from the individual components of thecomposites, but from gradients established at the interfaces between thecomponents. Ion exchange polymers with inherent microstructure, such asNafion, exhibit superior transport, selectivity, and stabilitycharacteristics compared to polymers with no inherent microstructure,such as poly(styrene sulfonate). When ion exchange polymers weresupported on inert substrates with microstructural (5 to 100 nm)features similar in length scale to the microstructural features of theion exchanger (e.g., 5 nm micelles in Nafion), the structure of the ionexchanger was disrupted in an ordered manner. The relationship betweenthe flux characteristics of the composites and the microstructureimposed by the substrates has yielded information about howmicrostructure contributes to the properties of ion exchangers. Thisrelationship allows the specification of design paradigms for tailoringcomposites with specific transport and selectivity characteristics.

Surface Diffusion

The first composites studied in this regard were formed by sorbingNafion into the collinear cylindrical pores of neutron track etchedpolycarbonate membranes. The ion exchange polymer, Nafion is aperfluorinated, sulfonic acid polymer with the following structure:

The SO₃ ⁻ groups adsorb on the inert substrates to form a loosely packedmonolayer of perfluorinated alkyl chains, OCF₂CF₂OCF₂CF₂SO₃ ⁻, shownabove in boldface. This creates a unique interfacial zone approximately1 to 2 nm thick along the edge formed between the ion exchange polymerand the inert substrate. In systems with high ratio of surface area tovolume, a large fraction of the molecules and ions which passed throughthese composites actually moved through this interfacial zone. That is,it was found that the molecules and ions have higher flux in this thininterfacial zone, where the interfacial fields were strongest.

In a given membrane, all pores had approximately the same diameter, d,ranging between 15 and 600 nm. The flux of electro-active speciesthrough the composites was determined by rotating disk voltammetry. Inrotating disk voltammetry, the product κm (cm²/s) parameterizes the fluxof a redox species through the Nafion portion of the composites, where κis the partition coefficient of the species into the Nafion and κm(cm²/s) is its mass transport coefficient. Simple Nafion films castdirectly onto the electrode were also studied. The resulting plots of κmas a function of log (d) are shown in FIG. 4A. As indicated in FIG. 4A,as the pore diameter decreased towards 30 nm, the flux through theNafion portion increased as much as 3600% over the simple films. Thesestudies showed that the interface between Nafion and a support matrixwas pivotal in determining the flux characteristics of the composites.

The flux enhancement model proposed here depends on the interface formedbetween the Nafion and the polycarbonate providing a facile transportpathway to the electrode for the redox species. Bulk Nafion located inthe center of the pore had a smaller transport coefficient (m) than thesupport matrix wall, but provided a volume to extract redox species fromthe center of the pore to feed the wall transport zone. The criticalparameter for flux enhancement was found to be (for a cylindrical crosssection path) the ratio of the surface area of the wall providing faciletransport (πdλ), where λ is the layer thickness, to the volume of Nafionfeeding the interface (πd²λ/4), i.e., 4/d. Plots of κm versus 1/d areshown in FIG. 4B. Note that the plots are linear in FIG. 4B for d≧30 nm,and with the exception of dopamine, the intercepts as d→∞ (1/d→0)correspond to κm for bulk Nafion.

Predictive models of how interfaces and their associated concentration,field, etc. gradients dictate interface properties and function areprovided below and further aid in the design of new composites tailoredfor specific applications. A simple surface diffusion model assuming nolimitations to the transport rate in the radial direction is outlined.FIGS. 5A and 5B show the simple model where transport in the radialdirection is not rate limiting. In the model, J_(comp) is the total fluxthrough the composites, J_(Nuc) is the flux through an empty pore, andJ_(bulk) and J_(wall) are the fluxes in the bulk (center) of the poreand along the surface of the pore, respectively. To analyze the flux, asin FIG. 4B, J_(bulk) and J_(wall) must be normalized to the crosssectional area of the pore used to determine κm, the product of theeffective extraction and transport coefficients. From the finalequation, the plot in FIG. 4B can be interpreted to have the slope andintercept shown in FIGS. 5A and 5B. If δ, the thickness of theinterfacial zone, is taken as 1.5 nm, the values cited forκ_(wall)m_(wall) and κ_(bulk)m_(bulk) are found. The diffusioncoefficients of each species in solution are also listed for comparison.In general, κ_(wall)m_(wall)≅(10 to 10²)×κ_(bulk)m_(bulk)≅(1 to10)×D_(soln). In other words, for an interfacial zone thickness, δ, of1.5 nm, κ_(wall)m_(wall) is up to one order of magnitude higher thanD_(soln), and one to two orders of magnitude higher thanκ_(bulk)m_(bulk).

The interfacial transport zone occurs because of the irreversibleexchange of Nafion sulfonic acid groups to polycarbonate surface sitesto form a monolayer of inactive sulfonic acid groups. The side chainslinking the sulfonic acid sites to the Nafion backbone form a looselypacked monolayer along the pore wall which facilitates the flux throughthe transport zone compared to transport through the tortuousenvironment of bulk Nafion. Given the length of the chains, a δ value ofabout 1.5 nm is consistent with κ_(wall)m_(wall) (and κm/D_(soln))decreasing as transport is more hindered with increasing diameter of theredox species; i.e., κ_(wall)m_(wall) decreases as H₂Q (0.6 nm)>Ru(NH₃)₆³⁺ (0.8 nm)>DOP⁺ (0.8 nm)>FerN⁺ (1 nm). Discrimination between thesespecies has also been observed based on molecular shape in the neutrontrack-etched composites. For example, disk shaped molecules exhibithigher flux than comparably sized spherical molecules.

Radial Migration

The pore walls have a surface charge density of −0.2 μC/cm². For a 30 nmpore diameter composite, the corresponding charge is 0.5% of the totalcharge in the pore, and will have negligible effect on the number ofcations extracted from the solution to move into the pore. However, thesurface charge establishes a potential gradient (electric field) fromthe pore to the wall which tends to move positively charged ionsradially outward from the center of the pore to the wall. An issue iswhether this radial, interfacial potential gradient can be coupled tothe concentration gradient along the wall to enhance solute flux to theelectrode, as illustrated in FIGS. 6A and 6B.

The model was tested by varying the concentration of the electrolyte,nitric acid, from 0.50 to 0.01 M, for fixed dopamine concentration (2mM). Flux was determined by rotating disk voltammetry at 400 rpm for thebare electrode and at infinite rotation rate for the modified electrodes(See Table 1). The electrolyte concentration did not dramatically affectthe flux for the bare electrode, the 30 nm membrane containing noNafion, and the Nafion film.

TABLE 1 Flux (nmol/cm²s⁻¹) for Dopamine Oxidation at Various [H⁺][H⁺]_(soln) Flux_(unmodified) ^(400 rpm) Flux_(30 nm) Flux_(film)^(Nafion) Flux_(30 nm) ^(Nafion) 0.50 M 38.6 54.8 4.2 2.4 0.10 M 36.757.5 4.3 10.5 0.01 M 44.6 73.1 — 39.0

However, for the 30 nm Nafion composite a fifty-fold decrease inelectrolyte concentration led to >1600% increase in flux. Coupling ofradial flux, driven by the interfacial potential gradient, to surfacediffusion generates the enhancement. No enhancements were observed for asimilar study of neutral hydroquinone. It should be noted that onlycharged species move by migration; dopamine is charged, whilehydroquinone is not.

Since the selectivity coefficient for dopamine over protons is about 500in Nafion, decreasing the electrolyte concentration fifty-fold onlydecreases the dopamine concentration by 10%. The dramatic effectproduced by varying the proton concentration means that the protons, notthe dopamine, compensate the wall charge to establish the interfacialpotential gradient and enhance the radial flux of dopamine. This ispossible because the dopamine, a cationic amine, is heavily ion pairedto the sulfonic acid sites. With a dielectric constant of 20,substantial ion pairing can be anticipated in Nafion. Ion pairing mayexplain why the flux of cationic amines is lower than neutralhydroquinone as can be seen with reference to FIGS. 4A and 4B which showκm values for neutron-track etched polycarbonate/Nafion composites. FIG.4A shows κm versus log(d), where d is the pore diameter. κm increasesabove the values for bulk Nafion as d approaches 30 nm. Theconcentrations are 2 mM redox species and 0.1 M electrolyte forRuN+—Ruthenium (II) hexamine (□), H₂Q—Hydroquinone (Δ,∇), DOP+—Dopamine(∘), and FerN+—Trimethylaminomethyl ferrocene (⋄). The electrolyte isH₂SO₄ in all cases except for DOP+ and H₂Q(∇). Lines represent no modeland are only intended to indicate the trend in the data. FIG. 4B showsκm versus d⁻¹, where 4d⁻¹ is the surface area of the pore/volume ofNafion in the pore. As illustrated in FIGS. 6A and 6B, the slopes inFIG. 4B are indicative of the surface flux, and the interceptcorresponds to the flux in bulk Nafion. Note, all the redox speciesexcept hydroquinone are charged amines, and all have lower flux thanhydroquinone.

Vapor Phase Electrochemistry/Microstructure in Two-Dimensions

One way to alter microstructure is to reduce the conduction matrix fromthree to two-dimensions. A two-dimensional system is made by sulfonatingthe nonionic, polymeric insulator between the electrodes of amicroelectrode assembly. Conduction across the surface cannot be studiedin either an electrolyte solution or a pure solvent as the liquidprovides a conductive path between the electrodes. However, bysupporting the microelectrode assembly in an evacuated flask, andinjecting hydrogen or hydrogen chloride and a small amount (μL's) ofwater, conduction can be studied by electrolyzing the gas. In theselower dimensional systems, the role of the ion exchange site and itsconcentration, as well as the role of water in ionic conduction can bestudied. Preliminary studies were performed to study conduction throughsolvent layers adsorbed from the vapor phase across the nonionic surfaceof a microelectrode assembly. Electrolysis of gas phase solventsrequired the solvent to adsorb at greater than monolayer coverage tobridge the gap between the electrodes. Solvents with high autoprotolysisand acidity constants sustain higher currents than solvents less able togenerate ions. These studies provided information about gas phaseelectrochemical detection and systems as well as atmospheric corrosion.

Composites Formed with Polymerized Microspheres

To test the generality of flux enhancement by interfacial forces,composites of Nafion and polymerized polystyrene microbeads ormicrospheres were formed; diameters of 0.11 to 1.5 μm were used. FIGS.7A and 7B show κm of hydroquinone through polystyrene microbead/Nafioncomposites versus ratios of surface area of the microbeads to volume ofNafion. In particular, values of Km found for various ratios of beadsurface area for transport to volume of Nafion for extraction (SA/Vol)are shown for three different bead diameters. As for the neutron tracketched composites, linear plots were found, at least for the largersizes, with intercepts comparable to bulk Nafion. Of these sizes, 0.37μm beads exhibited the largest flux enhancement (600%). (Note: the terms“beads” and “microbeads” are used synonymously herein). FIG. 7A showsresults for composites formed with single size beads, where the ratio ofsurface area to volume was varied by varying the volume fraction ofbeads in the composites. Positive slopes are shown consistent with fluxenhancement by surface diffusion along the surface of the beads. Theintercepts are consistent with transport through bulk Nafion.

The fraction of microbeads or microspheres in the composite can bevaried and different sizes mixed to allow a continuous range of SA/Vol.In particular, FIG. 7B shows results for composites for a range ofSA/Vol with 50% total fraction of Nafion by volume in the film. κmincreases as SA/Vol increases to about 3.5×10⁵ cm⁻¹, analogous to1.3×10⁶ cm⁻¹ found for the neutron track etched composites (FIG. 4A).Scanning electron micrographs of the 50% Nafion, single bead sizecomposites showed packing of the 0.11 μm beads was different and mayaccount for the lower κm values found for d⁻¹>3.5×10⁵ cm⁻¹, where 0.11μm beads were used. FIG. 7B shows results for composites formed with 50%Nafion by volume. The ratio of surface area to volume was varied bymaking composites with beads of the same size and with beads of twodifferent sizes. Flux increases as the ratio of surface area to volumeincreases to 3.5×10⁵ cm⁻¹; at the highest ratio, the composite contains0.11 μm beads.

From the scanning electron micrographs, composites of beads larger than0.11 μm exhibit the self-similarity typical of fractal materials. Whenln(κm) for these beads is plotted versus log(d), where d is the beaddiameter, a linear plot with a slope of −0.733 was obtained; κm versusd^(−0.733) is shown in FIG. 8A. For diffusion on a fractal of finitelyramified structure (e.g., the Sierpinski gasket), this is the powerdependence expected for diffusion in a two-dimensional system. Thus,microbead composites exhibit transport typical of fractal diffusionalong the microbead surface. This system confirms that surface diffusionprovides a mechanism of flux enhancement. It also introduces the conceptof fractal transport processes and the importance of surfacedimensionality in ion exchange composites.

Poly(4-Vinylpyridine) Composites Formed on Neutron Track EtchedMembranes

To investigate surface diffusion in other ion exchangers, compositeswere formed of protonated poly(4-vinylpyridine) (PVP) and neutron tracketched membranes. Flux enhancements in these composites also increasedas the ratio of surface area of the pores to volume of PVP decreased.This result is consistent with the results found for Nafion composites,where facile surface transport enhanced flux.

Thermal Processing of Nafion

While commercial Nafion is heat (or hot) cast, a process that yieldsinverted micelles, the vast majority of academic studies of Nafion havebeen performed on cold cast Nafion which produces normal micelles. Astudy of the mechanical properties of Nafion hot cast from organicsolvents has been reported. Attempts have been made to hot cast Nafionfilms with microwave heating. In the highly ionic casting solution, theglass transition temperature of Nafion (105° C.) should be reached asthe water evaporates. Plots of flux as a function of the time microwavedhave a break at approximately 15 minutes. The flux changed by no morethan a factor of three with a decrease in the flux of hydroquinone, andfrom preliminary studies, an increase in the flux of Ru(NH₃)₆ ³⁺. Thismay indicate different transport mechanisms for the two species in thefilm. Microwaved, cold cast and commercial hot cast films have beencompared.

Magnetic, Demagnetized, and Nonmagnetic Composites

Polystyrene-coated, 1 to 2 μm Fe/Fe oxide (nonpermanent magneticmaterial) or organo-Fe (superparamagnetic or ferrofluid or permanentmagnetic) microbeads are available (Bangs Labs, Polyscience, orDelco-Remy) as a 1% suspension in water, and Nafion (C.G. Processing) isavailable as a 5% suspension in alcohol/water. Other inert or activepolymer coatings besides polystyrene, as well as non-polymeric materialsmay also be used as encapsulating materials for the microbeads ormagnetic particles. Examples of such encapsulating materials mayinclude, for example: various polymers, silanes, thiols, silica, glass,etc. On the other hand, in some situations a polymeric or other coatingmaterial on the microbeads or magnetic particles may be completelyeliminated, as described below. This discussion holds forsuperparamagnetic or ferrofluid or permanent magnetic or nonpermanentmagnetic or ferromagnetic or ferrimagnetic material microbeads ingeneral. This discussion also holds for other magnets and other magneticmaterials which include, but are not limited to, superconductors, andmagnetic materials based on rare earth metals such as cobalt, copper,iron, samarium, cerium, aluminum and nickel, and other assorted metaloxides, and magnetic materials based on neodymium, e.g., magnequench,which contains iron and boron in addition to neodymium.

Under certain circumstances, some microbeads or magnetic particles foruse in carrying out the invention may require coating with, e.g. apolymeric material. For example, in aqueous environments a coating of aninert material may serve to inhibit or prevent oxidation of themicrobead material. In other circumstances the application of a coatingto the microbead material is not required (see, for example, the sectionbelow on Iron Oxide Microbead Composites).

Magnetic composites incorporating organo-Fe material microbeads areformed by casting appropriate volumes of each suspension onto anelectrode centered inside a cylindrical magnet (5 cm inside diameter,6.4 cm outside diameter, 3.2 cm height; 8 lb pull). Once the solventsevaporate and the magnet is removed, the oriented beads are trapped inthe Nafion, stacked in pillars normal to the electrode surface. Tominimize interbead repulsion, pillars form by stacking the north end ofone bead to the south end of another; to minimize interpillar repulsion,the pillars arrange in a roughly hexagonal array. These alignedcomposites were formed with microbead fractions of ≦15%. Alignedcomposites were compared to other composites: unalignedcomposites—formed as above but with Fe/Fe oxide microbeads and withoutthe magnet; nonmagnetic composites—formed with 1.5 μm nonmagneticpolystyrene beads; simple Nafion films; and demagnetizedcomposites—aligned composites that were demagnetized. Demagnetizedcomposites had the pillared structure, but it is not clear if they werefully demagnetized. Nonmagnetic composites had a coral-like structure(i.e., they do not form pillars). Note, composites may be formed whereinat least one component is reversibly changeable between a paramagneticform and a diamagnetic form with, for example, a temperature variationand with or without the presence of an externally applied magneticfield.

Iron Oxide Microbead Composites

Magnetic composites comprising particles of various materials, such as,for example iron oxides, encapsulated or coated with a polymeric orother inert material may be used to modify the interface of electrodesurfaces to provide systems or devices with new and improvedcharacteristics. Such systems and devices lend themselves to a broadrange of useful and commercially valuable applications including, butnot limited to, the separation of transition metal species from otherspecies, and improved fuel cells and batteries.

Composites formulated for the purpose of surface modification ofelectrodes may also comprise non-coated (naked or uncoated) particles ofmaterials such as iron oxides. The preferred iron oxides, under theinvention, are iron(III) oxide (Fe₂O₃) and magnetite (Fe₃O₄). Electrodeswith surface modifications employing composites which comprisenon-coated iron(III) oxide or non-coated magnetite provide fluxenhancements comparable in magnitude to those produced by coated(encapsulated) magnetic particles. Indeed, from a theoreticalstandpoint, uncoated (i.e. non-coated) magnetic particles are expectedto yield higher flux enhancements than similarly sized coated magneticparticles; the coating on encapsulated particles increases the distancebetween the source of the magnetic field and the reactant moleculesand/or ions, and thus the effect of the decaying magnetic field isdiminished.

These results, showing flux enhancements with composites comprisingnon-coated magnetic particles, suggest that a large variety of magneticmaterials may be readily incorporated into composites without the needfor coating or other specialized preparatory step(s). In this regard, itshould be noted that the use of non-coated particles eliminates much ofthe cost (perhaps in the region of 50%) of the cost of manufacturingmagnetic composites. At the same time, these results indicate that othermagnetic materials, with stronger fields than iron-based magnets, may besimilarly incorporated into composites to produce even larger effects.

Iron oxides such as aged Fe₂O₃ are chemically inert and insoluble inmost solvents, suggesting that composites comprising iron oxides exhibitsufficient durability for many commercial applications.

Composites comprising non-coated magnetic particles are formed in amanner similar to that reported herein for the formation of compositescomprising encapsulated (coated) magnetic particles. The difference isthat non-coated magnetic materials, such as those described below, areused in place of the coated (encapsulated) magnetic microbeads orparticles. In the case of particles of iron (III) oxide, material thathas “aged” to some extent is preferred over freshly prepared iron (III)oxide. Apparently, the surface of slightly aged iron oxide materialshave a surface behavior similar to that observed for polyethylene, afairly inert material. Newly prepared iron oxide appears to be moresusceptible to reaction with solution species than aged material.

Composites were formed with 15% by volume iron(III) oxide (Fe₂O₃)(Aldrich Chemical Co.) and Nafion. The composites are formed by castingthe Nafion and the magnetic material (here, uncoated iron oxideparticles with diameters of a few microns) onto the electrode surface.An external magnetic field, such as that provided by an externalcylindrical magnet, may be positioned around the electrode at thisstage. When an external magnet is used, the casting mixture dries as afilm which includes pillared magnetic structures on the surface of theelectrode, as described in more detail elsewhere herein. The externalmagnet, if any, is removed.

Other percentages of iron(III) oxide and Nafion, as well as other ironoxides (e.g., Fe₃O₄) and other magnetic materials may also be used informing such composites, provided that the magnetic material ischemically inert in the proposed environment in which it is to be used.For example, under the invention, magnetic composites may be formedcomprising from 85% to 0.01% by weight of magnetic material, and from15% to 99.99% of an ion exchange polymer. The magnetic materialcomponent in the casting mixture which is used to make-up the compositemay be in the form of magnetic particles, beads or microbeads of ironoxides (e.g. Fe₂O₃, Fe₃O₄), and may be coated or non-coated(encapsulated or non-encapsulated). Depending on the application, thecomposite may optionally further comprise carbon particles, or otherelectron conductors, in association with a catalyst. The amount ofelectron conductor, e.g. carbon particles, in association with acatalyst in the composite, according to the invention, may range from 0%to about 80% by weight (or mass). An example of carbon particles inassociation with a catalyst according to the invention is carbonparticles in association with platinum (i.e. platinized carbon).

An electrode with surface modifications including a composite comprising15% by volume of non-coated iron(III) oxide, and prepared as describedabove, was placed in a solution of ruthenium (III) hexamine (aparamagnetic species with one unpaired electron) as redox probe, and theflux was measured by cyclic voltammetry. An electrode bearing a film ofNafion only was used for comparative purposes. The results are presentedin FIG. 8B, in which two voltammograms are shown. Voltammogram 1 is forthe electrode bearing a simple film of Nafion coated on the surface ofthe electrode. Voltammogram 2 is for an electrode bearing the compositecomprising Nafion and 15% non-coated particles of iron(III) oxide. Itcan be seen from FIG. 8B that the current at approximately −350 mV isabout 3 times as large in voltammogram 2 as compared to voltammogram 1.Also, the peak potential differences are smaller in the case ofvoltammogram 2, suggesting some impact on the rate of the reaction.Similar narrowing of the peak splitting has been observed for all of themagnetic materials we have tested (both coated and non-coated).Composites comprising magnetic materials of the type described above mayprove useful in facilitating or catalyzing a broad range of surfacechemical reactions, both electrochemical and otherwise.

Other Composites

Similar effects to composites formed with Nafion have been observedusing a different polymer and a solvent other than water. One suchsystem is poly(styrene sulfonate) (PSS) in acetonitrile solvent. Theelectrolyte is tetraalkylammonium tetrafluoroborate which is differentthan the inorganic electrolytes that were used in water. Redox probesthat have also been used in this system, include Fe(bpy)₃ ²⁺ andFe(bpy)₃ ³⁺. Some additional redox species that have been used as probeswith these PSS composites (magnets on electrodes) include Fe(II)(bpy)₃²⁺, Fe(III)(bpy)₃ ³⁺, Co(II)(bpy)₃ ²⁺, and Co(III)(bpy)₃ ³⁺.

Magnetic Composites Electrochemical Studies of Magnetic Composites

A composite was equilibrated in a solution of 1 mM electro-activespecies and 0.1 M electrolyte. The mass transport-limited current forthe electrolysis of the redox species through the composite (i_(meas))was then determined by steady-state rotating disk voltammetry at severaldifferent rotation rates (ω). A plot of i_(meas) ⁻¹ versus ω⁻¹ yielded aslope characteristic of transport in solution, and an interceptcharacteristic of transport through the composite as: $\begin{matrix}{\frac{nFA}{i_{meas}} = {{\frac{v^{1/6}}{0.62\quad c*D_{soln}^{2/3}}\omega^{{- 1}/2}} + \frac{l}{\kappa \quad m\quad \varepsilon \quad c^{*}}}} & (3)\end{matrix}$

In Equation (3), n is the number of electrons, F is the Faradayconstant, A is the electrode area, c* and D_(soln) are the concentrationand diffusion coefficient of the redox species in solution,respectively, ν is the kinematic viscosity, l is the compositethickness, κ is the partition coefficient of the redox species, m is themass transport rate of the redox species in the composite, and ε is theporosity of the composite. The partition coefficient, κ, is the ratio ofthe equilibrium concentration in the ion exchange portion of thecomposite to the solution concentration, in the absence of electrolysis.Equation (3) is appropriate for rate-limiting transport perpendicular tothe electrode. This is ensured by choosing l and D^(1/3)_(soln)ω^(1/2)ν^(1/6) large compared to the microstructural dimensionsof the composite, and is verified by the slope. Then, the composite canbe treated as homogeneous with an effective κm, and microstructuraleffects can be ascertained with rotating disk studies. Cyclicvoltammetry yielded quantitative information for scan rates, v,sufficient to contain the transport length within the composite. For areversible couple, the peak current, i_(peak), is given by equation (4):

i _(peak)=0.4463(nF)^(1/2) [v/RT] ^(1/2),  (4)

where R is the gas constant and T is the temperature. When both rotatingdisk and cyclic voltammetry data are obtainable, κ and m are separablebecause of their different power dependencies in Equations (3) and (4).

The flux of redox species through magnetic composites is enhanced inproportion to the absolute value of the difference in the magneticsusceptibilities of the products and reactants of the electrolysis. Fromcyclic voltammetry, the ΔE_(p) observed for reversible species, whetherparamagnetic or diamagnetic, was little changed, but E_(0.5) wasshifted, where E_(0.5) is the average of the anodic and cathodic peakpotentials, and is a rough measure of the free energy of the electrontransfer reaction. For a quasireversible, diamagnetic species whichpassed through a radical intermediate, dramatic changes in ΔE_(p) werefound. The shifts and peak splittings were consistent with thestabilization and the concentration of the paramagnetic species. Resultsare summarized below.

Flux Enhancements for Paramagnetic Species

Values of κm found by rotating disk voltammetry for diamagnetichydroquinone and Ru(bpy)₃ ²⁺, and paramagnetic Ru(NH₃)₆ ³⁺ using Nafionfilms, nonmagnetic polystyrene microbead composites, and magneticmicrobead composites are summarized in Table 2. Both bead compositescontained 15% beads of 1 to 2 μm diameter; all modifying layers were 3.6to 3.8 μm thick.

TABLE 2 km (10⁻⁶ cm²/s) for Various Magnetic/Nonmagnetic Species andFilms km_(Nafion film) km_(Nonmagnetic) km_(magnetic) Hydroquinone 0.9251.02 2.21 Ru(bpy)₃ ²⁺ 0.290 0.668 0.869 Ru(NH₃)₆ ³⁺ 0.570 1.01 3.80

Table 2A shows cyclic voltammetric results for other species. Theseresults are summarized in FIG. 9.

In these examples, as in general, when flux of redox species through themagnetic composite was compared to flux through either Nafion films orcomposites formed with nonmagnetic beads, the flux was enhanced. Ingeneral, we find the flux enhancement is not dependent on whether theelectrolysis is converting a diamagnetic to a paramagnetic species or aparamagnetic to a diamagnetic species, but that the enhancementincreases as the absolute value of the difference in the molar magneticsusceptibilities of the product and reactant.

To further investigate paramagnetic Ru(NH₃)₆ ³⁺, κm values were foundfor magnetic and nonmagnetic composites made with various fractions ofbeads. Results are shown in FIG. 10. First, in FIG. 10 the flux ofRu(NH₃)₆ ³⁺ increased strongly with the fraction of magnetic beads, butnot with the fraction of nonmagnetic beads. Second, since theenhancement is not linear with the magnetic bead fraction, theenhancement was not due to either a simple concentration increase of theparamagnetic species about each bead or a simple increase in surfacediffusion associated with more pillars at higher bead concentration.(Data are equally well linearized with correlation coefficient >0.99 aseither ln[κm] versus percent beads, or κm versus volume ofNafion/surface area of the beads. Plots of both showed interceptscomparable to κm for simple Nafion films.) Third, substantially higherflux was achieved with the magnetic beads than with the same fraction ofnonmagnetic beads.

In another series of experiments, composites were formed with magneticmicrobeads of similar size, but containing different amounts of magneticmaterial. In these studies, as magnetic content increased, the values ofκm and κm^(1/2) increased. The magnetic content was measured with a Guoybalance and is characterized by χ_(bead) (see FIG. 11).

Magnetohydrodynamic models neither account for the discriminationbetween paramagnetic and diamagnetic species by the magnetic composites,nor do they predict the shape of the curve shown in FIG. 10.Magnetohydrodynamics predicts an effect proportional to the charge onthe redox probes. No such dependence is found here.

Electrochemical flux of various redox species from solution througheither composites or films to the electrode surface was determined bycyclic and steady-state rotating disk voltammetry. Electrochemical fluxof species through the composites is parameterized by κ and m, where κis the extraction coefficient of the redox species from solution intothe composite, and m (cm²/s) is its effective diffusion coefficient. Forsteady-state rotating disk voltammetry, the parameterization is κm(determined from the intercept of a Koutecky-Levich plot); and forcyclic voltammetry, the parameterization is κm^(1/2) (extracted from theslope of peak current versus the square root of the scan rate (20 to 200mV/s). All measurements were made in solutions containing 1 to 2 mMredox species at a 0.45 cm² glassy carbon electrode. The electrolyte was0.1 M HNO₃, except for the reduction of Co(bpy)₃ ²⁺ (0.2 M Na₂SO₄) andfor the oxidation of Co(bpy)₃ ²⁺ and reduction of Co(bpy)₃ ³⁺ (0.1 Msodium acetate/acetic acid buffer at pH=4.5). Anionic ferricyanide wasnot detected electrochemically through the anionic Nafion films andcomposites, consistent with defect-free layers. All potentials wererecorded versus SCE (SCE is a standard calomel reference electrode; ithas a standard potential of −0.24 V with respect to the reductionpotential of hydrogen ions to hydrogen molecule at unit activity).

First, κm values were determined for the oxidation of paramagneticRu(NH₃)₆ ³⁺ to diamagnetic Ru(NH₃)₆ ²⁺ through magnetic and nonmagneticcomposites as the bead fraction was increased. |Δχ_(m)|=1,880·10⁻⁶cm³/moles. From FIG. 10, κm for the nonmagnetic composites varies littlewith bead fraction, while κm for the magnetic composites increasessuperlinearly by several fold.

Second, κm^(1/2) values were determined for various redox reactions formagnetic composites, nonmagnetic composites, and Nafion films. Exclusiveof any magnetic field effects, electrochemical flux through Nafion canbe altered by the size, charge, and hydrophobicity of the transportedspecies, interaction and binding with the exchange sites, andintercalation into the hydrated and perfluorinated zones of the Nafion.To minimize effects not related to interactions between the redoxmoieties and the magnetic beads, κm^(1/2) values for the magnetic andnonmagnetic composites are normalized by κm^(1/2) for the Nafion films.The normalized κm^(1/2) values are plotted in FIG. 9 with error barsversus |Δχ_(m)| for the various redox reactions. FIG. 9 illustrates therelative flux of redox species on the y-axis, where the maximum cyclicvoltammetric current for a composite with magnetic microbeads isnormalized by the maximum cyclic voltammetric current for a Nafion filmcontaining no magnetic material. The ratio is the flux enhancement. Onthe x-axis is the absolute value of the difference in the molar magneticsusceptibilities of the products and reactants of the electrolysis,|Δχ_(m)|. The composites contain 15% magnetic microbeads and 85% Nafionby volume. The redox species are numbered as follows, where the reactantproducts are listed sequentially: (1) hydroquinone to benzoquinone; (2)Cr(bpy)₃ ³⁺ to Cr(bpy)₃ ²⁺; (3) Ru(bpy)₃ ²⁺ to Ru(bpy)₃ ³⁺; (4) Ru(NH₃)₆³⁺ to Ru(NH₃)₆ ²⁺; (5) Co(bpy)₃ ²⁺ to Co(bpy)₃ ¹⁺; (6) Co(bpy)₃ ²⁺ toCo(bpy)₃ ³⁺; and (7) Co(bpy)₃ ³⁺ to Co(bpy)₃ ²⁺. All redox species are 1mM to 2 mM. Film thicknesses are 3.6μ to 3.8 μm. For the nonmagneticcomposites, the normalized κm^(1/2) values are independent of |Δχ_(m)|.This suggests the normalization is effective in minimizing steric andelectrostatic differences in the interactions of the various redoxspecies with Nafion. For the magnetic composites, normalized κm^(1/2)increases monotonically with |Δχ_(m)|, with the largest enhancementsapproaching 3000%.

The logarithmic increase of electrochemical flux in FIG. 9 with |Δχ_(m)|is consistent with a free energy effect of a few kJ/mole. Effects ofthis magnitude have not been generated in uniform, macroscopic magneticfields. Strong, nonuniform magnetic fields established over shortdistances (a few nanometers) at the interface between Nafion andmagnetic microbeads could produce local effects of this magnitude.Magnetic concepts appropriate to uniform macroscopic magnetic fields andto molecular magnetic interactions are not applicable to this system,and instead, a microscopic parameterization is necessary. Establishingsufficiently strong and nonuniform local magnetic fields at interfacesin microstructured systems makes it possible to orchestrate chemicaleffects in micro-environments which cannot otherwise be achieved withuniform fields applied by large external magnets.

Cyclic Voltammetric Peak Splittings for Quasireversible Species

Peak splittings in cyclic voltammetry are used to determinedheterogeneous electron transfer rates. FIGS. 12A and 12B show cyclicvoltammetric results for the reversible species Ru(NH₃)₆ ³⁺ and Ru(bpy)₃²⁺, respectively. Cyclic voltammograms at 100 mV/s are shown forRu(NH₃)₆ ³⁺ (FIG. 12A) and Ru(bpy)₃ ²⁺ (FIG. 12B) for magneticcomposites, Nafion films, and the bare electrode. Cyclic voltammetricresults are shown for the reduction of paramagnetic Ru(NH₃)₆ ³⁺ in FIG.12A. The concentration of the redox species is 1 mM, and the electrolyteis 0.1 M HNO₃; the reference is an SCE; and the films are 3.6 μm thick.For both species, when E_(0.5) is compared for the magnetic compositeand the Nafion films, the shift in E_(0.5) is to positive potentials.The electron transfer kinetics for Ru(NH₃)₆ ³⁺ are fairly strong withk⁰>0.2 cm/s. Note that the peak splittings for the magnetic compositesand Nafion film are similar, consistent with the resistance of the twolayers being similar. Similar peak splittings are also observed forRu(bpy)₃ ²⁺, as shown in FIG. 12B. Therefore, when compared to theNafion films, the magnetic composites have little effect on the rate ofelectron transfer of reversible species.

In particular, FIG. 12C shows cyclic voltammograms at 100 mV/s for 1 mMhydroquinone in 0.1 M HNO₃ for magnetic composites, nonmagneticcomposites, Nafion films, and the bare electrode. The films are 3.6 μmthick. It is observed in the voltammogram of FIG. 12C that the peaksplitting is almost doubled for the magnetic composite compared to theNafion film. The question arises as to whether the enhanced peaksplitting is consistent with the stabilization of the paramagneticsemiquinone intermediate in the two electron/two proton oxidation. InFIG. 12C, voltammograms are shown at 0.1 V/s for hydroquinone, adiamagnetic species that undergoes quasireversible, two electron/twoproton oxidation to diamagnetic benzoquinone while passing through aradical, semiquinone intermediate. The voltammograms for the Nafion filmand the nonmagnetic composites are fairly similar, with ΔE_(p) values of218 and 282 mV, respectively. For the magnetic composite, ΔE_(p)=432 mV,or twice that of the Nafion film. From the results for the reversiblecouples above, this is not due to a higher resistance in the magneticcomposites. The asymmetry in the peak shifts compared to the other threesystems shown in FIG. 12C also argues against a resistance effect. (Notethat the interpretation of the kinetics can be complicated by the protonconcentration. However, there is no reason to think the concentration isdrastically different in the magnetic and nonmagnetic composites.) Thepeak shift may be due to the stabilization of the paramagneticsemiquinone intermediate.

While the hydroquinone electrolysis is too complex to interpret cleanly,it does raise the interesting question of whether quasireversibleelectron transfer rates can be influenced by an applied magnetic field.Reversible rates will not be affected, but it is not clear what wouldhappen with quasireversible rates. There are many quasireversibleelectron transfer species uncomplicated by homogeneous kinetics anddisproportionation reactions which can be used to better resolve thisquestion. If the kinetics of quasireversible processes can be influencedby magnetic fields, numerous technological systems could be improved.Oxygen reduction by two and four electrons are examples of a systemwhere quasireversible kinetics may be susceptible to alteration by anapplied magnetic field gradient.

Cyclic Voltammetric Peak Shifts

When magnetic composites and Nafion films were compared, voltammogramstaken at 0.1 V/s for the reversible species exhibited no change inΔE_(p). However, the peak potential for reduction, E_(p′) ^(red), forRu(NH₃)₆ ³⁺ was shifted 14 mV positive. Similarly, the oxidationpotential peak, E_(p) ^(ox), for Ru(bpy)₃ ²⁺ was shifted 64 mV positive.Shifts of E_(0.5) while ΔE_(p) is unchanged are consistent with onespecies being held more tightly in the composites, and thereby, having alower diffusion coefficient. In general, a shift in potential ofapproximately +35 mV is observed for all reversible redox species,whether the electron transfer process converts the redox species fromdiamagnetic to paramagnetic or paramagnetic to diamagnetic. Largerpotential shifts are observed with less reversible electron transferprocesses. Shifts as large as 100 mV have been observed. (Note that forthe film thicknesses used herein (≅3.6 μm) and a scan rate of 0.1 V/s,m≦10⁻⁸ cm²/s is needed for the diffusion length to be confined withinthe film during the sweep. Since m is not known in these systems, it isnot clear whether the voltammetric results also probe behavior at thecomposite/solution interface.)

The above discussion further shows that interfacial gradients other thanconcentration and electric potential, e.g., magnetic gradients, can beexploited effectively in microstructured matrices. In composites formedwith magnetic materials, locally strong (and nonuniform) magnetic fieldscould alter transport and kinetics. The influence of the magnetic fieldon species in composites may be substantial because the species areconcentrated in a micro-environment, where the distance between thefield source and chemical species is not large compared to the fielddecay length. Magnetic composites were made by casting films ofpolystyrene coated magnetic beads and the perfluorinated, cationexchange polymer, Nafion, onto an electrode. Approximately 1 μm diametermagnetic beads were aligned by an external magnet as the castingsolvents evaporated. Once the solvents evaporated and the externalmagnet was removed, the beads were trapped in the Nafion, stacked asmagnetic pillars perpendicular to the electrode surface.

Preliminary voltammetric studies comparing the magnetic composites tosimple Nafion films (i.e. containing 0% magnetic microbeads) yieldedseveral interesting results. First, flux of redox species throughmagnetic microbead composites is enhanced compared to flux through bothsimple Nafion films (i.e. Nafion alone) and composites formed withnonmagnetic microbeads. Second, for species which underwent reversibleelectron transfer (i.e., Ru(NH₃)₆ ³⁺ and Ru(bpy)₃ ²⁺), the cyclicvoltammetric peak potential difference (ΔE_(p)) was unaffected, but theaverage of the peak potentials (E_(0.5)) shifted consistent with thestabilization of the paramagnetic species. Third, hydroquinone oxidationwas quasireversible and proceeded through paramagnetic semiquinone. Forhydroquinone at 0.1 V/s, voltammograms for the magnetic compositesexhibited a 40 mV positive shift of E_(0.5) and a ΔE_(p) twice that ofNafion. The potential shifts and flux enhancements, while consistentwith concentration and stabilization of the paramagnetic form of theredox couples, are as yet unexplained.

Electrochemical flux of ions and molecules through magnetic compositesformed of Nafion ion exchange and polystyrene coated Fe/Fe oxideparticles has been observed to be as much as twenty-fold higher than theflux through simple Nafion films. Flux enhancements have been observedwith increasing difference in the magnetic susceptibility of the halvesof the redox reaction.

A passive, magnetic composite may be used to enhance the flux of oxygenat the cathode in a fuel cell. Oxygen has two unpaired electrons, and istherefore susceptible to this magnetic field in the same way asdescribed in the experiments above. If oxygen is consistent with theobservations made thus far for other ions and molecules, theelectrochemical flux of oxygen to a magnetically modified cathode can beenhanced by approximately 500% as compared to a nonmagnetically modifiedcathode (FIG. 13). Such an enhancement would be comparable to thatachieved by pressurization to 5 atmospheres at the cathode.

Based on the above discussion, it is possible to predict a roughlyfive-fold flux enhancement of oxygen through a 15% magnetic/Nafioncomposite over Nafion. This is understood by considering the fluxesthrough magnetic/Nafion composites and Nafion films of the seven redoxspecies listed in the upper left hand corner of FIG. 13. These are thesame species as listed in FIG. 9. The fluxes were determined by cyclicvoltammetry. The flux ratio for magnetic composites to Nafion films isthe y-axis and the absolute value of the difference in the molarmagnetic susceptibilities (|Δχ_(m)|) of products and reactants of theelectrolysis reaction is the x-axis of FIG. 13. (The larger the value ofΔχ_(m), the more susceptible a species is to interaction with a magneticfield.) From FIG. 13, the flux increases exponentially as |Δχ_(m)|increases. For the most extreme case, the flux is increased abouttwenty-fold. For the reduction of oxygen to water, |Δχ_(m)|≈3500·10⁻⁶cm³/mole. This point on the x-axis is extrapolated to therefore suggestthat the flux enhancement for oxygen in the magnetic composite willapproach five-fold.

Experiments have been conducted with Nafion composites of up to 15%Fe/Fe oxide particles or beads. FIG. 14 shows a curve of the increase influx based on the percentage of magnetic beads. The dotted line on FIG.14 is the projected effect on flux of higher bead concentrations.

For paramagnetic species, the flux through the magnetic compositesincreases as the fraction of magnetic beads increases. In FIG. 14, theflux of Ru(NH₃)₆ ³⁺ through magnetic bead/Nafion composites ()increases as the fraction of magnetic beads in the composite isincreased to 15%. Larger enhancements may be possible with higher beadfraction composites or composites formed with magnetic beads containingmore magnetic material. Compared to a simple Nafion film (□), the fluxis 4.4 fold larger. Ru(NH₃)₆ ³⁺ is less paramagnetic than oxygen. Forcomparison, composites formed with nonmagnetic polystyrene beads (◯)were examined; these exhibited no flux enhancement as the bead fractionincreased. The line shown on the plot is generated as a logarithmic fitto the data for the magnetic composites. It illustrates the fluxenhancement that might be found for composites formed with a higherfraction of magnetic beads. The extrapolation suggests that at 30%magnetic beads, the flux through the magnetic composites of Ru(NH₃)₆ ³⁺might approach twenty times its value in simple Nafion films. As oxygenis more paramagnetic than Ru(NH₃)₆ ³⁺ even larger enhancements might beanticipated for oxygen.

Oxygen Susceptibility to Magnetic Composites and Magnetic Concepts

Paramagnetic molecules have unpaired electrons and are drawn into(aligned by) a magnetic field (i.e., a torque will be produced; if amagnetic field gradient exists, magnetic dipoles will experience a netforce). Radicals and oxygen are paramagnetic. Diamagnetic species, withall electrons paired, are slightly repelled by the field; most organicmolecules are diamagnetic. (Metal ions and transition metal complexesare either paramagnetic or diamagnetic.) How strongly a molecular orchemical species responds to a magnetic field is parameterized by themolar magnetic susceptibility, χ_(m) (cm³/mole). For diamagneticspecies, χ_(m) is between (−1 to −500)·10⁻⁶ cm³/mole, and is temperatureindependent. For paramagnetic species, χ_(m) ranges from 0 to +0.01cm³/mole, and, once corrected for its usually small diamagneticcomponent, varies inversely with temperature (Curie's Law). While ionsare monopoles and will either move with or against an electric field,depending on the sign of the potential gradient (electric field),paramagnetic species are dipoles and will always be drawn into (alignedin) a magnetic field, independent of the direction of the magneticvector. A net force on a magnetic dipole will exist if there is amagnetic field gradient. The magnetic susceptibilities of O₂, H₂O andH₂O₂ are summarized in Table 3.

TABLE 3 Molar Magnetic Susceptibilities, _(Xm) Species Temperature (⁰K)X_(m) (10⁻⁶cm³/mole) O₂ 293 3449 H₂O 293 −13 H₂O₂ — −18

Magnetic field effects were observed in electrochemical systems. Becauseelectrochemistry tends to involve single electron transfer events, themajority of electrochemical reactions should result in a net change inthe magnetic susceptibility of species near the electrode. Little hasbeen reported, however, in electrochemistry on magnetic fields. What hasbeen reported relates to magnetohydrodynamics. Magnetohydrodynamicsdescribes the motion of the charged species (i.e., an ion) perpendicularto the applied magnetic field and parallel to the applied electric field(Lorentz force). In the composites described herein, the magnetic field,the direction of motion, and the electric field were all normal to theelectrode. Because magnetohydrodynamics (see FIGS. 1-3) does not predicta motion dependence on the magnetic susceptibility of the moving speciesand requires that all the field and motion vectors are perpendicular(i.e., for magnetic effects), the effects described here are unlikely tobe macroscopic magnetohydrodynamic effects.

Graded Density Composites

The following protocol is used to form density layers on electrodes withthe density layers parallel to the electrode surface or other surface:Solutions of Ficoll (a commercially available copolymer of sucrose andepichlorhydrin used to make macroscopic graded density columns forseparations of biological cells by their buoyancy) are made in water atconcentrations varying from a few percent to 50% by weight. Theviscosity of the solution is a monotonic function of the weight percentpolymer. Small volumes of polymer solution (5 to 100 μl) are pipettedonto an electrode surface and the electrode spun at 400 rpm for twominutes; this creates a single polymer layer. By repeating this processwith polymer solutions of different concentrations, a graded interface,with density and viscosity varied as a function of the composition ofthe casting solution or casting mixture, can be created. The thicknessof each step in the staircase structure depends on the number of layerscast of a given concentration, and can range from 200 nm to severalmicrometers.

A similar structure with graded layers of ion exchange sites in ionexchange polymers can be formed by either (1) spin casting or coating amixture of density gradient polymer and ion exchange polymer on theelectrode or other surfaces as described above; (2) forming a densitygraded layer of density gradient polymer first, and then adsorbing theion exchange polymer into the matrix; or (3) spin casting or coatinglayers of ion exchange polymer on surfaces from solutions of differentconcentrations. It should be possible to cast such layers, and then peelthem off surfaces to form free standing films. Such films would haveutility in controlling solvent transport across electrochemical cells,including fuel cells.

A protocol is proposed to form density gradient layers on electrodeswith the density layers perpendicular to the electrode surface or othersurface. Electrodes and surfaces can be envisioned in which more thanone gradient is established on the surface for purposes of separatingmolecules in more than one spatial and temporal coordinate and by morethan one property. One example is to form composites with a magneticgradient in one coordinate and a density gradient in another coordinate.These materials could be formed by creating a magnetic gradientperpendicular to the electrode surface by placing magnetic beads on anelectrode or surface and allowing the composite to be cast in anonuniform field, where the external magnet is aligned so the beads areon the surface but not in columns perpendicular to the surface. Adensity layer could be cast (as opposed to spun cast or coated) bypipetting small volumes of different concentrations of density gradientpolymer and/or ion exchange polymer and allowing the solvents toevaporate, thereby building up a graded layer parallel to the electrodesurface. Once the entire layer is cast, the external magnet can beremoved if the magnetic material is superparamagnetic, and left in placeif the magnetic material is paramagnetic.

These would be fairly sophisticated composites, and complex tounderstand, but unusual flux enhancements and separations should bepossible in several dimensions. It should be possible to design evenmore complex structures than these. For example, embodiments may combinetwo effects such as magnetic field gradient effects with densitygradient effects to make a more sophisticated separator to performmultiple separations of similar materials. This would be an example ofan apparatus and method for separating similar things in a mix whichinvolves a graded matrix instead of separate chambers (such as forlighter transition metals and heavier transition metals or other speciesas discussed below).

Modified Ion Exchangers

The surface of the magnetic microbeads have ion exchange groups on themwhich would allow ready chemical modification, e.g., coating with amagnetically oriented liquid crystal for a local flux switch.Embodiments of such modified structures may have use in the quest tobuild microstructured devices and machines.

Separation of Lanthanides and Actinides

Lanthanides and actinides are the heaviest transition metals havingatomic numbers in the ranges 58-71 and 90-103, respectively. Thelanthanides and actinides include metals such as plutonium, uranium, andthorium. Various isotopes of these transition metals are radioactive,and either are used as the fissionable material in nuclear reactors orare generated by nuclear decay processes.

Some of the isotopes of lanthanides and actinides (e.g., ²²⁷Ac, ²³²Th,²³⁵U, ²³⁸U, ²³¹Pa, ²³⁷Np, ²⁴⁴Pu, ²⁴²Pu, ²³⁹Pu, ²³⁸Pu, ²⁴³Am, ²⁴¹Am,²⁴⁴Cm, ²⁴²Cm, ²⁴⁹Bk, and ²⁵²Cf) have significant (long) half-lives, andpose a significant environmental remediation problem, especially whenthe radioactive materials are present in a complex matrix of wastesludge or mine tailings. A most extreme example is the storage vats atHanford, Washington. Thus, separation of lanthanides and actinides isimportant. Note, separation here means separation of ions and metalsrather than isotopes.

The environmental problems could at least be simplified if the heaviertransition metals could be removed selectively from the matrix. Even ifthe separation process simultaneously removes metal species other thanthe lanthanides and the actinides, the separation would still beadvantageous. The separation does not have to be specific, onlyselective, to be useful. For example, removing the heavier transitionmetals from the waste sludge greatly reduces the level of radioactivehazard in the remaining sludge. The separated radioactive material wouldbe concentrated and much reduced in volume, and, therefore, easier tocontain.

Radioactive isotopes are also employed in various imaging processes,especially for medical diagnosis. These processes typically use isotopeswith half-lives of a few days or hours. Therefore, isotopes must begenerated either on-site or elsewhere to be shipped and used rapidly. Iflonger half-life isotopes could be used, some of these constraints mightbe simplified. Also, better images could be obtained with higherconcentrations and stronger emitters of radioactive material. Currently,higher concentrations are not used because the detoxification protocolinvolves isotope decay in the body, rather than a removal process.Therefore, if a method for removing the heavy transition metals from thebody could be developed, the range with respect to the type andconcentration of isotopes could be expanded.

Difficulty of Separating Lanthanides and Actinides

All of the prior discussion of FIGS. 10 to 14 apply to the lightertransition metals which have been studied. However, the notionsconcerning magnetism discussed so far in relation to FIGS. 10 to 14(which directly support these notions) may also apply to the heaviertransition metals as well. The heavier transition metals (lanthanidesand actinides) are expected to have similar properties to the lightertransition metals, only more exaggerated.

The lanthanides and actinides have high nuclear mass, and thedifferences in the chemistries of these heavier transition metals ineither row of the periodic chart is established by the number ofelectrons in the fourth and fifth f-shells, respectively. However, thef-shell electrons are shielded by the fifth (lanthanide) and sixth(actinide) s- and p-shell electrons, and the chemistries of the metalsin each row of heavier transition metals are not highly differentiated.

Although traditional methods for separating metals and metal ions arebased on selectively plating the metal ions, or using variouschromatographic methods, these methods have not been very successfulwith lanthanides and actinides. Plating methods are not successfulbecause the reduction potentials of the lanthanides and actinides areall within 200 millivolts of each other. For the lanthanides, the threeelectron reduction of the trivalent cation to the metal occurs at−2.3+0.1 Volts versus NHE (normal hydrogen electrode—a referenceelectrode defined to the thermodynamic scale of 0 Volts for protonreduction as is well-known in the art) for all the members of theseries.

Separations can be achieved by various methods, based on, amongst otherthings, charge, mobilities, and complex formation with chelating agents.Chromatographic separations can be driven, amongst other things, bycharge and mobilities. For heavier transition metals such as lanthanidesand actinides, charge-based chromatographic separations will not workbecause these transition metals all have similar charge and similarreduction potentials, which means that they will have similar chargeeven after they are all reduced. The same redox potential means that youcannot selectively reduce or oxidize only some of the species.

Because the lanthanides and actinides form similarly sized ions, themobilities are all very similar, and species, therefore, cannot bewell-separated by mobility. Nonchromatographic separation methodsinvolving chelating methods will also be difficult. For example, as thef-shell electrons are shielded by the s- and p-electrons of the nextprincipal shell, the binding constants of the ions of either series withvarious chelating agents are very similar, resulting in species notbeing well-separated by chelation. Therefore, another separationtechnique for these series, such as magnetic separation, is required.

Magnetic Separations of Lanthanides and Actinides

The response of a molecule or ion to a magnetic field is measured by itsmolar magnetic susceptibility (χ_(m)) or equivalently, by its magneticmoment, μ. As the number of unpaired electrons in the species increases,μ increases. The lanthanides and actinides have f-shell electrons, whichcan contain between 0 and 14 electrons. Therefore, the maximum number ofunpaired electrons in the f-shell is 7. The properties of the lightertransition metals in the main body of the periodic table are such thatthey have only d-shell electrons, which can number as many as 10 with amaximum number of five unpaired electrons. Inherently, therefore,lanthanides and actinides can have higher numbers of unpaired electronsthan the transition metals with only d-shell electrons. Thus,lanthanides and actinides can have higher magnetic moments thantransition metals from the main body of the periodic table. The highermagnetic moments arise from unpaired electrons and, to some extent,nuclear magnetic moments. The higher magnetic moments, as well as thegreater range in oxidation states (prior discussion of paramagnetic anddiamagnetic redox species is applicable here) and should allowlanthanides and actinides to be separated from the lighter transitionmetals. In some cases, this separation may require an additionaloxidation and/or chelation step.

In particular, if a separation yields a mixture of heavier transitionmetals and transition metals from the main part of the periodic table(lighter transition metals), a change in oxidation state, achieved byeither adding an oxidant or reductant or by electrolysis at anelectrode, will change not only the charges (and number of electrons inthe d- (for main transition metals) and f-shells (for heavier transitionmetals)) on the metal ions or their complexes, but it can also changethe number of unpaired electrons in the heavier and main transitionmetals. Because the main transition metals have only 10 d-shellelectrons and the heavier transition metals have 14 f-shell electrons,ions, metals and complexes which have at least a few electrons in eitherthe d- or f-shells are likely to have different numbers of unpairedelectrons when electrons are added or removed. This will allow the maintransition metals to be separated from the heavier transition metals ina large number of cases.

Plots of magnetic moments for the lanthanides, actinides, and lightertransition metals are appended in FIGS. 14A, 14B, and 14C, respectively,for representative metal ion complexes. FIGS. 14A and 14B were taken,respectively, from pp. 329 and 369 of “Advanced Inorganic Chemistry” byF. A. Cotton and G. Wilkinson, Third Edition, Interscience Publishers,NY, 1972, the contents of which are incorporated herein by reference.Data for FIG. 14C were taken from pp. 38-239 of “The Magnetic Propertiesof Transition Metal Complexes” by B. N. Figgis and J. Lewis in “Progressin Chemistry,” vol. 6, F. A. Cotton, ed., Interscience Publishers, NY,1964 and from F. H. Burstall and R. S. Nyholm, J. Chem. Soc., 1952, pp.3570-3579, both of which are incorporated herein by reference. Anexamination of FIGS. 14A-C shows that the magnetic moments of theheavier transition metals are higher than those of the lighter metals.Clearly, however, there is some overlap of magnetic moments between thetwo categories of transition metals. For example, Cr(III), UF₄, UF₃, andPr₂O₃ have similar magnetic moments, as do Cr(II) and PuF₄. Themagnetically-based separation would, therefore, not distinguish verywell between these species, and they may be grouped together before andafter the separation step.

However, additional separation steps involving chelation or electrolysisbefore a subsequent separation step would certainly remove the lightertransition metals from the heavier ones. Nevertheless, the separation ofuranium from plutonium species might be more difficult, because themethod may not be sufficiently selective. Additional tuning of themethod might improve the separation, or repetitive separations mighthelp. Even without additional improvements, it is at least possible toseparate trivalent and tetravalent uranium and plutonium species fromspecies such as iron, for example.

One possible way to separate some heavier transition metal species is touse the fact that they can form gaseous species and that certainseparations lend themselves to the gas phase. For example, separation ofthe gas UF₆ (uranium hexafluoride) or various isotopes thereof may beaccomplished using such a separation technique. Previously, isotopes ofuranium were separated by making UF₆ and allowing the gases to diffusedown extremely long tubes. Because of the slight differences in mass,the lighter isotopes got to the end of the tubes first.

It should be noted that temperature could have a very great effect onwhat drives magnetic separations in general and, in particular, whatdrives magnetic separations of heavier transition metals. Operation atlower temperature can be a real advantage because magneticsusceptibility (moment) of molecular species increases as reciprocaltemperature. Dropping temperature from room temperature to just abovefreezing increases the magnetic moments about 10% (see the discussionabout Curie Temperature above). Perhaps this temperature sensitivity maybe exploited with thermal gradients to drive magnetic separations ofheavy transition metals and other magnetic species.

It is also possible to build a sensor based on the temperaturesensitivity, including a sensor for hot (radioactive) heavier transitionmetals. A differentiation of some of the various radioactive species ina mix may be realizable from (1) flux enhancement and (2) temperatureincreases. Perhaps a combination of flux enhancement andtemperature-based magnetic separation could be made with parallel orperpendicular magnetic and thermal gradients.

Achieving Separations

Separations can be thought of in several steps:

1. Species are separated because they have different degrees ofinteraction with some external agent or force (here, magnetic compositesand magnetic fields).

2. If one interaction enhances separations, but it does not achievecomplete separation, the process should be repeated to improveseparation efficiency (here, it may be necessary to set up a sequence ofseparation vats and magnetic composite separators)..

3. If, after several iterations, separation has been partiallysuccessful, but several species are still mixed together, try anotherseparation process on this mixture which has already been refined by thefirst process (here, this could be a, for example, a chelation processto bind either the lighter or heavy transition metals, e.g., toselectively precipitate one set or the other, or a plating process mightbe used, or a change in oxidation states followed by another separationstep, based on either magnetic properties or some other properties).

For the present invention, the principles described herein may beapplied in conjunction with the use of magnetic composites to separatelanthanides and actinides from other metal ions and to separatelanthanides and actinides into smaller groups based on their magneticmoments. The behavior and formation of one class of magnetic compositeshas been previously outlined above.

Based on the previously demonstrated behavior of these composites withthe lighter transition metal complexes, it should be possible toseparate the heavy transition metal ions or complexes formed bychelation thereof with organic or inorganic ligands. It may be ions,metals, or metal complexes (charged and uncharged) which can beseparated, although ions and organometallic complexes are most likely.

The efficiency of the separation will be prescribed, at least in part,by the magnetic moment of the species separated. In anelectrochemically-based process, the efficiency may be dictated by thedifference in the magnetic moments of the oxidized and the reduced formsof the species. Two basic separation processes are outlined:

Electrochemical processes in which a magnetic composite controls accessof the species in the solution to the electrode.

Magnetochromatographic processes in which a magnetic composite is usedas a separation membrane between two vats, where one vat has the mixtureto be separated, and the species to be separated passes through theseparator to a second vat, where the selectively passed or separatedspecies are collected.

Either of the above processes are possible processes for achieving theseparation. Other chromatographic processes, where the carrier is a gas,liquid, solid, or plasma and the stationary phase is any magneticallymodified microstructured material, also possibly a gas,liquid/suspension, solid, or plasma, are feasible. Here, the roles ofthe carrier and the stationary phase are not differentiated and may beinterchanged.

Single step separations are possible either chromatographically orelectrochemically. However, in a multistep process, as will most likelybe needed, several chambers or vats are set up in sequence asillustrated in FIG. 14D so that the most mobile species will beconcentrated in the last vat. Here, the magnetic separator may be eithersimply chromatographic or it may be a magnetically modified porouselectrode that allows flow through the electrode. In FIG. 14D which willbe discussed in detail below, the separator lets species A pass throughthe separator with twice the efficiency of species B. After threeseparation steps, the concentration of species A is enhanced 8:1([2/1]³:1) compared to species B, where species A and B were in equalconcentrations initially. The efficiencies of magnetic separators willdepend on the magnetic properties of the species being separated asdiscussed above and should be at least as good as the situation justillustrated. Note that the initial, relative concentrations of thespecies in the initial mixture, like species A and B, will also play arole.

It may be necessary to add ligands before or after the magneticseparation. Ligands added before separation may change selectivitythrough a separation membrane, probably for reasons other than magneticproperties. For example, if binding is favored for the lightertransition metal species and they can be bound to form negativelycharged lighter transition metal complexes, these complexes would beexcluded from the composites if a positively charged ion exchangepolymer, or equivalent positively charged material, were used as thebinder to form the composite.

It is also possible to increase the magnetic moment of some transitionmetal complexes if ligands are used which force the metal center toswitch from a low to a high spin electron configuration. Lower magneticmoments can be achieved if the ligands force the metal center into thelow spin configuration. Cobalt is the most common example of a speciescapable of forming low and high spin complexes. However, not all metalshave low and high spin configurations.

Ligands may be added after the separation, where the selective bindingto a ligand would allow the chemistries of the lanthanides and theactinides to be distinguishable from the lighter transition metalspecies. For example, if large binding constants allow the actinides andthe lanthanides to form complexes with large ligands, the lanthanidesand actinides might be precipitated selectively from the mixture. Otherseparation processes are also possible. Magnetic separations involvingligands may be applied to lanthanides and actinides as will be discussedin detail below (see discussion involving FIGS. 16A, 16B, and 16Cbelow).

APPLICATIONS OF THE INVENTION General Applications

FIG. 15A shows a simplified representation which will be used todescribe how magnetic microboundaries 10 a, 10 b, and 10 c influence astandard electrochemical process. Here, a substrate 20 with a surface 24serves as a conductor and hence can electrically conduct like a metal, asemiconductor or a superconductor. Substrate 20 is maintained at a firstpotential V1. Two different phases of materials 30 a and 30 b have twodifferent magnetic fields, i.e., are in two different magnetic phases,phase 1 and phase 2 and are applied to surface 24 of substrate 20. Sincematerials 30 a and 30 b have different magnetic fields, boundary regionsor boundaries 33 have magnetic gradients. Boundary regions 33 are notnecessarily sharp or straight, but the magnetic field of material 30 asmoothly changes into the magnetic field of material 30 b according toelectromagnetic boundary conditions. Therefore, width t represents anaverage width of boundaries 33. Width t should be approximately betweena few nanometers to a few micrometers and preferably between onenanometer and approximately 0.5 μm. Boundary regions 33 are separatedfrom each other by varying distances and S represents the average ofthese distances. The effect of varying distances S will be describedbelow.

Particles M have a magnetic susceptibility χ_(m) and are in anelectrolyte 40 which is at a potential V2 due to an electrode 50. Thismakes a potential difference of V between electrolyte 40 and substrate20 (substrate 20 can effectively act as a second electrode). Boundaryregions 33 are paths through which particles M can pass. Particles M arethen either driven electrically or via a concentration gradient towardsubstrate 20. Once particles M reach substrate 20, they either acquireor lose electrons, thereby turning into particles N with magneticsusceptibility χ_(n). The absolute value of the difference between themagnetic susceptibilities of phase 1 and phase 2 is a measure of themagnitude of the magnetic gradient in region 33 and will be referred toas the magnetic gradient of boundary region 33. It will be shown belowthat the flux of particles M increases approximately exponentially withrespect to increasing the magnetic gradient of boundary region 33 withmaterials 30 a and 30 b when compared to the flux without materials 30 aand 30 b. This increase in flux can be greater than 35-fold or 3500%,resulting in significant improvements in efficiency of manyelectrochemical processes.

Specific examples of electrochemical systems where magnets might improvean electrochemical cell or process include: chloralkali processing,electrofluoridation, corrosion inhibition, solar and photocells ofvarious types, and acceleration of electrochemical reactions at theelectrode and in the composite matrix. Potential shifts of E_(0.5) arealways observed and suggest an energy difference is generated by themagnetic fields and gradients in the composites; generically, this couldimprove performance of all electrochemical energy devices, includingfuel cells, batteries, solar and photocells. Other applications include,sensors, including dual sensors for paramagnetic species; opticalsensors; flux switching; and controlled release of materials by controlof a magnetic field, including release of drugs and biomaterials, or inmedical dosing. There may also be applications in imaging and resonanceimaging technologies.

Boundaries 33 do not have to be equally spaced and do not have to haveequal widths or thicknesses t. Materials 30 a and 30 b can be liquid,solid, gas or plasma. The only restriction is that a boundary 33 mustexist, i.e., materials 30 a and 30 b must have two different magneticfields to create the magnetic gradient within the width t. The magneticgradient of region 33 can be increased by (1) increasing the magneticcontent of the microbeads; (2) increasing the magnetic microbeadfraction in the composite; (3) increasing the magnetic strength of thebeads by improving the magnetic material in the beads; and (4) enhancingthe field in the magnetic microbeads by means of an external magnet. Ingeneral, the flux of particles M and N is correlated with magneticsusceptibility properties, χ_(m) and χ_(n). The above phenomena can beused to improve performance of fuel cells and batteries.

FIG. 15B shows apparatus 80 which corresponds to any of the abovediscussed embodiments as well as the embodiments shown in FIG. 16 orthereafter. The implementation of some of the embodiments of theinvention requires the presence of a magnetic field such as thatproduced by electromagnet 70, while other embodiments may not requireelectromagnet 70. Apparatus 80 corresponds to, for example, someembodiments of the magnetically modified electrode, the fuel cell, thebattery, the membrane sensor, the dual sensor, and the flux switch.Electromagnet 70 can be any source of a magnetic field. Electromagnet 70can also be used in the above discussed methods of forming the compositemagnetic materials that require the presence of an externally appliedmagnetic field. Electromagnet 70 can be controlled by controller 72 toproduce a constant or oscillating magnetic field with power supplied bypower supply 74.

An external magnetic field such as could be applied by electromagnet 70may be useful in various embodiments of the invention. Switches andfurther enhancements might be possible in cases where the external fieldis concentrated in the magnetic microbeads or particles. For example,flux switches might be useful, especially as actuated by an externalmagnet or electromagnet 70 in such applications as: (1) release ofmaterials in medical applications; (2) recollection of hot isotopes inmedical imaging applications as explained above; (3) microreactors andseparators as a means of mixing—perhaps to control a micronuclearreactor or a heat source driven by hot materials; and (4) make are-usable system for cleaning and collecting heavier transition metalsin hot storage tanks.

For this last idea, once something is contaminated with a hot(radioactive) material, it becomes radioactive itself, and is handled aswaste to be stored or cleaned. Since cleaning is a complex issue that isnot completely presently understood and since there is a major emphasison controlling the amount of contact with hot materials, an alternativeembodiment might be small heavy transition metal “scrubbers” havinglocated therein magnetic separators, flux switches, and/or otherexamples of structures described herein. These scrubbers would bejettisoned or dispensed into a radioactive tank (or other environment),allowed to collect the heavy transition metals (radioactive or not),then recollected and allowed to release their contents by turning on/offtheir flux switches. One way the scrubbers could be caused to releasetheir magnetically held materials would be to increase the temperaturebecause magnetic effects are reduced at higher temperatures. Theswitches would then be reset and the scrubbers repositioned orredispensed to scrub again. There would be no new waste and thescrubbers would provide a collector/cleaner/concentrator.

The scrubbers could be exposed to the species to be collected or thespecies could be distributed amongst the scrubbers by flowing thespecies over, through, past, or amongst the scrubbers. Moreover, thescrubbers could be contained in a container, released externally tocollect the species to be collected, then be recollected within thecontainer for releasing the collected species, and then be recycled orre-used to collect more of the species. It should be understood that thescrubbers of this type need not be restricted to heavier transitionmetal applications or storage tanks. For instance, the scrubbers may beemployed to “scrub” or remove uranium ions and salts from mine tailings.

FIG. 16 shows another simplified diagram showing a second manifestationof the above described phenomenon and hence a second broad area ofapplication. Namely, FIG. 16 shows a separator 60 disposed between afirst solution 62 a and a second solution 62 b. Here, there is noelectrode or conductive substrate 20. Solution 62 a has at least twodifferent types of particles M₁ and M₂ with two different magneticsusceptibilities χ_(m1) and χ_(m2), respectively. Once particles M₁ orM₂ drift into an area near any one of boundaries 33, they areaccelerated through the boundaries 33 by the magnetic gradient therein.Here, χ_(m1) is greater than χ_(m2), which causes the flux of particlesM₁ through separator 60 to be greater than the flux of particles M₂through separator 60. This difference in flux can again be greater than3500%, and may will tend to cancel out or override any difference inacceleration due to different masses of particles M₁ and M₂.Consequently, if the above process is allowed to proceed long enough,most of the particles M₁ will have passed through separator 60 beforeparticles M₂, thereby making first solution 62 a primarily made up ofparticles M₂ and second solution 62 b primarily made up of particles M₁.Note, separation of particles M₁ and M₂ may require some specialtailoring of the separator 60 and also depends on how much time isallowed for particles M₁ and M₂ to separate. In an infinite amount oftime, both particles M₁ and M₂ may cross separator 60. Particle size mayalso have a bearing on the ultimate separation of particles M₁ and M₂ byseparator 60.

The above discussion with respect to FIG. 16 involves two types ofparticles, M₁ and M₂, but the discussion also holds for any number ofparticles. Consider, for example, solution 62 a having particles M₁, M₂,M₃ and M₄ with susceptibilities χ_(m1), χ_(m2), χ_(m3) and χ_(m4),respectively. If χ_(m1)>χ_(m2)χ_(m3)>χ_(m4), then M₁ would pass moreeasily through separator 60, followed by M₂, M₃ and M₄. The greater thedifference between magnetic susceptibilities, the better the separation.Multistep chamber separations employing various separators likeseparator 60 with similar or different properties may also be envisionedas will be discussed below.

The above phenomenon can be used to improve performance of fuel cellsand batteries. Other applications include separation technology ingeneral, chromatographic processes—including separation of highertransition metal species (lanthanides and actinides), and photography.

To more particularly illustrate the relevant ideas for the magneticseparation of lanthanides and actinides as previously discussed, furtherconsideration of FIG. 14D is appropriate. FIG. 14D shows a system 950having a series of vats, i.e., vat 1, vat 2, vat 3, and vat 4 (althoughany number of vats are possible). Between each of vats 1-4 are magneticseparators with magnetic separator 960 between vat 1 and vat 2, magneticseparator 970 between vat 2 and vat 3, and magnetic separator 980between vat 3 and vat 4. Magnetic separators 1-4 may be of the same typeor each a different type. Any one of magnetic separators 960, 970, or980 may also be a membrane, a porous electrode, or a magneticallymodified electrode. A combination of a porous electrode or amagnetically modified electrode with other types of magnetic separatorsmay be possible.

Species or particles A and B are initially in a mixed state or mixture990A in vat 1 in FIG. 14D in equal or unequal concentrations. The ideais to separate species or particles A from species or particle B byusing the selectivity of the combination of vats 1-4 and magneticseparators 960, 970, and 980 (in some circumstances a single magneticseparator like magnetic separators 960, 970, or 980 and two vats likevats 1-4 may suffice for separating species). The properties of magneticseparators 960, 970, and 980 are such that species or particles Apreferentially and selectively pass therethrough. Over time, or byvirtue of this selectivity, the concentration of species or particles Aincreases in vat 4 as the separation proceeds from vat 1 having mixture990A therein to vat 2 having mixture 990B therein, and then from vat 2to vat 3 having mixture 990C therein, and then finally from vat 3 to vat4 having mixture 990D therein. Mixtures 990A, 990B, 990C, and 990D ofspecies or particles A and B become more pure in species or particles Aas the separation proceeds from vat 1 to vat 4 with vat 4 having mixture990D of species or particles A and B most pure in species or particlesA.

It is possible that vat 4 may contain species or particles A alone(allowing for other impurities) in mixture 990D and no species orparticles B. It is also possible that as the concentration of species orparticles A is maximized relative to the concentration of species orparticles B in mixture 990D in vat 4, simultaneously the converse may beoccurring in mixture 990A in vat 1 as species or particles B are leftbehind by species or particles A, although this is not required. Avariation of how the accumulation of species or particles B in mixture990A in vat 1 occurs is to have preferential transport of species orparticles B from any and all of vats 2-4 toward vat 1. For example, bothmixture 990A in vat 1 and mixture 990D in vat 4 may include species orparticles A and B initially in some initial concentrations. Due to theproperties of magnetic separators 960, 970, and 980 and over a period oftime, the concentration of species or particles A increases in mixture990D in vat 4 while the concentration of species or particles Bincreases in mixture 990A in vat 1 over their respective initialconcentrations. The net transport of species or particles A and B istowards vat 4 from vats 1-3 and towards vat 1 from vats 2-4,respectively.

FIGS. 16A, 16B, and 16C illustrate possible uses of ligands in theselectivity of a separation. Ligands 995 may be involved to aid in theselectivity of the separation, whether ligands 995 are used in mixtures990A-D or with any component thereof, i.e., species or particles A or B,or they are bound to or used in some way in magnetic separators 960,970, or 980. FIG. 16A depicts ligands being used to preferentially aidin the transport of species or particles A from mixture 990A in vat 1 tomixture 990D in vat 4. In vat 1, ligands 995 form complexes 996 withspecies or particle A. Complexes 996 are preferentially transportedthrough magnetic separators 960, 970, and 980. Once complexes 996 reachvat 4, a decoupling of ligands 995 and species or particles A may or maynot occur (it is shown to occur in FIG. 16A). Of course, an alternativeembodiment (not shown) would be to have ligands 995 form complexes withspecies or particles B instead, such complexes preventing species orparticles B from being transported from vat 1 having mixture 990Aultimately to vat 4 having mixture 990D while species or particles A areso transported.

Another alternative embodiment is shown in FIG. 16B, wherein ligands 997are associated with magnetic separators 960, 970, and 980 to formcomplexes 998 with either of species or particle A and B so as to allowonly one of these species or particles to be transported from vat 1 tovat 4. FIG. 16B illustrates complexes 998 formed with species orparticles A that allow transport of species or particles A throughmagnetic separators 960, 970, and 980. It is understood that any ofmagnetic separators 960, 970, or 980 may instead have associated ligands997 form complexes 998 with species or particles B that prevent speciesor particles B from passing therethrough while the passage of particlesA is not so prevented.

FIG. 16C shows another embodiment wherein lighter transition metals Cand heavy transition metals D such as the heavy transition metallanthanides and actinides are separated from a mixture 990E in vat 1that includes other species or particles E. This separation throughmagnetic separator 960A leaves mixture 990F in vat 2. Once this firstseparation occurs, heavy transition metals D are then separated fromlighter transition metals C with the use of ligands 999A formingcomplexes 1000 with either lighter transition metals C or heavytransition metals D (complexes 1000 with heavy transition metals D areshown in FIG. 16C). In FIG. 16C complexes 1000 pass through magneticseparator 970A more easily than the lighter transition metals D, thisseparation leaving mixture 990G in vat 3. In FIG. 16C magneticseparators 960A and 970A are shown separating vat 1 from vat 2 and vat 2from vat 3, respectively.

FIG. 16D shows an alternative embodiment without magnetic separator 970Aor vat 3 having mixture 990G. In this embodiment starting from mixture990E in vat 1, magnetic separator 960A separates lighter transitionmetals C and heavier transition metals D from other species or particlesE leaving mixture 990F in vat 2. In vat 2 ligands 999C form complexes1000A only with heavy transition metals D. Complexes 1000A facilitatethe precipitation of heavy transition metals D as precipitate 1001 asshown in FIG. 16D. In this way heavy transition metals D are separatedfrom lighter transition metals C. Note that in facilitating theprecipitation of heavy transition metals D as precipitate 1001,complexes 1000A may or may not precipitate along with heavy transitionmetals D (i.e., complexes 1000A may or may not separate into ligands999C and heavier transition metals D while the precipitation isoccurring). It is to be understood that other ligands that are differentfrom ligands 999A or 999C may be used in addition to ligands 999A or999C to form complexes with lighter transition metals C to aid in theseparation of lighter transition metals C from heavier transition metalsD, although this is not shown in either FIGS. 16C or 16D.

All of the embodiments discussed above in relation to FIGS. 14D, 16A,16B, 16C, and 16D correspond to the embodiments shown in FIGS. 16 and 19and discussed herein which were also included in the parent application,i.e., copending U.S. application Ser. No. 08/294,797 filed Aug. 25,1994.

Additional variations of the illustrations involving differentconfigurations of vats, magnetic separators, mixtures, and/or ligands orchelating agents may be envisioned by those skilled in the art. Thesevariations include the use of different magnetic separators between anyof the vats, different ligands within each vat forming complexes withparticular species or types of species therein, different ligandsassociated with any of the magnetic separators that form complexes withparticular species or types of species, or other vectors or separatorsin 2 or 3 dimensions, or any other variations that would occur to thoseskilled in the art.

More complex systems than those illustrated in FIGS. 16A-16D may beenvisioned to separate materials, e.g., combined density gradients,thermal gradients, magnetic composite gradients, etc. (with or withoutvectorial transport), but not limited thereto. For example, complexmatrices may be employed if there exists a mixture having iron speciesand heavier transition metals therein. In these matrices, by separatingaccording to size and weight, it may be possible to better separatethese materials from other materials. After the initial separation,separation of iron from the heavier transition metals would be enhancedin the matrices by specifically adding charge and change of charge withthe use of electrolysis. Iron is more readily electrolyzed than theheavier transition metals, so despite being collected in the initialseparation with the heavier transition metals, it can be removed byelectrolysis to either plate out, or change its number of unpairedelectrons so as to change its magnetic moment, whereby it could beseparated out on the next step.

In the above discussion with respect to FIGS. 15 and 16, the greater thenumber of boundary regions 33 per unit area (i.e., the smaller S), thegreater the effects due to the presence of boundary regions 33macroscopically manifest themselves. S can vary from fractions of amicrometer to hundreds of micrometers. In quantum systems with smallerstructures, S is further reduced to less than approximately 10 nm.

Design paradigms are summarized below to aid in tailoring composites forspecific transport and selectivity functions:

Forces and gradients associated with interfaces, which are of noconsequence in bulk materials, can contribute to and even dominate thetransport processes in composites.

Increasing the microstructure of composites can enhance the influence ofinterfacial gradients.

The closer a molecule or ion is placed to the interface, the strongerthe effect of the interfacial field on the chemical moiety. Systemsshould be designed to concentrate molecules and ions near interfaces.

The ratio of surface area for transport to volume for extractionparameterizes surface transport.

Fields in a microstructural environment can be nonuniform, but locallystrong.

Strong but short range electrostatic and magnetic fields are betterexploited in microstructured environments than in systems withexternally applied, homogeneous fields.

Vectorial transport is plumbed into microstructured matrices by couplingtwo or more field or concentration interfacial gradients, the resultbeing advantageous compared to homogeneous matrices; the largest effectswill occur when the gradients are either perpendicular or parallel toeach other.

Control of surface dimensionality (fractality) is critical in optimizingsurface transport in composites.

Several advantages are inherent in ion exchange composites over simplefilms. First, composites offer properties not available in simple films.Second, composites are readily formed by spontaneous sorption of the ionexchanger on the substrate. Third, while surfaces dominate manycharacteristics of monolayers and composites, three-dimensionalcomposites are more robust than two-dimensional monolayers. Fourth;interfaces influence a large fraction of the material in the compositebecause of the high ratio of surface area to volume. Fifth, compositesoffer passive means of enhancing flux; external inputs of energy, suchas stirring and applied electric and magnetic fields, are not required.Sixth, local field gradients can be exploited in composites because thefields and molecular species are concentrated in a micro-environmentwhere both the decay length for the field and the microstructuralfeature length are comparable. In some of the composites, the field maybe exploited more effectively than by applying an homogeneous field to acell with an external source.

SPECIFIC EXAMPLES Fuel Cells

It would be very beneficial to achieve high efficiencycompressor/expander power recovery technology. One way to improve theefficiency of the compressor/expander would be to reduce the pressurerequirement. If a passive pressurization process could be providedwithin a fuel cell itself, at no cost to the power output of the fuelcell, power production from present day fuel cells would be increased byapproximately 20%.

Magnetically modified cathodes may reduce the need for pressurization asoxygen is paramagnetic. The field may also alter oxygen kinetics asdiscussed below. Potential shifts of +35 mV to +100 mV represent a 5% to15% improvement in cell efficiency and comparable savings in weight andvolume. Also, in fuel cells, as hydrated protons cross the cell, thecathode floods and the anode dehydrates. Water transport may bethrottled by composite separators of graded density and hydration.

In addition to the probability of enhancing flux at a magneticallymodified electrode, oxygen reduction kinetics in the case of fuel cellsmay be altered. The kinetics for oxygen reduction are outlined here:

There is a difficulty with the oxygen reduction kinetics that arises, inlarge part, because H_(2l O) ₂ (peroxide) desorbes as peroxide insolution, and does not dissociate on the catalyst surface to form 2OH.Peroxide is not paramagnetic, but HO₂ and OH are paramagnetic. However,the presence of a magnetic field will tend to stabilize the HO₂, slowingthe formation of peroxide. Once adsorbed peroxide is formed, themagnetic field will shift the equilibria in a direction that favors theformation of 2OH. This should drive a larger fraction of the reactingmolecules toward the formation of water, where the full potential ofoxygen reduction can be realized as discussed above in regard to E⁰_(cathode) for water formation and E⁰ _(H2O2). For these reasons, oxygenwill be susceptible to the enhancements that have been observed fromother similar paramagnetic species as discussed above.

It may also be important to make a fuel cell with little or no thermalsignature, especially in an environment, where, for instance, a minimalthermal signature would be beneficial. Fuel cells are operated attemperatures approaching 100° C. to improve kinetic efficiency. Whilethis temperature is much lower than the temperatures of other refuelablepower sources such as internal combustion engines (about 400° C.), 100°C. is still hotter than the human body (about 37° C.) or ambienttemperature. However, if kinetic efficiency is improved by amagnetically modified cathode, then fuel cell operating temperatures canbe lowered toward ambient temperature without substantial effect onpower output. Also, magnetic effects will be larger at lowertemperatures. A fuel cell mounted on highly thermal conductivematerials, like materials used on the Space Shuttle, might be a way tomaintain its temperature closer to body or ambient temperature. Notethat although a reduced thermal signature and a reduced operatingtemperature may be desirable for a fuel cell, there may be an optimaloperating temperature for the fuel cell based on performanceenhancements, and the method of reducing the thermal signature may haveto be accommodating thereof.

The following summarizes some of the salient advantages and features ofan ambient pressure PEM fuel cell in operation according to the instantinvention:

Reduces the weight of the fuel cell system by removing the compressorpumps;

Reduces the size of the fuel cell system by removing compressor pumpsand reduces the size of the fuel cell stack required to reach the sameoutput power;

Allows the production of fuel cells that are ⅜ inches thick and asflexible as a plastic transparency;

Increases the efficiency of the fuel cell system by 20%;

Increases the voltage—may be driven by a positive shift in the cathodepotential or improved kinetics associated with shorter lifetimes of H₂O₂adsorbed on the electrode surface with the reaction equilibria shiftedtoward formation of OH;

Reduces the likelihood of system failure by removing all mechanicalparts, i.e., removing mechanical pumps;

Lowers operating temperature—reduces the thermal signature by improvingthe performance at lower operating temperatures; fuel cells are normallyrun at higher temperatures to improve the oxygen reduction kinetics, butif kinetic enhancement occurs, then the fuel cell operating temperaturecan be lowered without a net performance reduction; magnetic effects arelarger at lower temperatures which may increase the flux of oxygen evengreater and, therefore, make up for performance deficits associated withlower fuel cell operating temperature;

Is scalable—can be used with the same effect on any size fuel cellstack; and

Increases the mean time between failures (MTBF) of the power system byremoving mechanical pumps.

It is important to recall that the above advantages and benefits areachieved while eliminating the need for compressor pumps. Also, if thepotential shift or kinetic enhancement are not realized to their fullyanticipated degree, then the fuel cell will still operate moreefficiently with the flux enhancement that is produced. The minimumresult will be a fuel cell that operates at the same performance levelof current fuel cells without the added weight of the compressor pumpsand the 15% parasitic power loss associated with running the pumps.

In a PEM fuel cell (or in any other apparatus requiring an electrodedescribed herein or otherwise) it may also be beneficial to tailor theelectrode-magnetic composite interface for electrical conductivity. Forexample, the direct coating of the magnetic beads of the composite withplatinum or any other conductor, or semiconductor, or superconductor maysignificantly increase electrical conductivity of the interface over arandom mixing of magnetic beads with fixed quantities of carbon andplatinum (or any other conductor, or semiconductor, or superconductor(e.g. carbon) and catalyst (e.g. platinum), hereinafter referred tosimply as electron conductor plus catalyst). It would then be possibleto test and evaluate oxygen reduction at magnetically and electricallymodified electrodes made with platinum-coated magnetic microbeads mixedwith carbon.

Platinum coating of the beads could be accomplished by sputteringplatinum on the beads or by any means known in the art. The oxygenreduction results of the directly coated bead system may be compared tooxygen reduction at electrodes made by mixing carbon and platinum powderwith magnetic beads, and a determination made as to whetherplatinum-coated beads offer significant enhancement over the simplemixture. To optimize the magnetic bead fraction and platinum content,the point at which increasing the platinum content does notsignificantly increase oxygen reduction would be determined, as well asthe point at which increasing the magnetic bead content (fraction) doesnot increase flux or becomes unstable. All the above results would becompared to similar results obtained for platinum electrode-magneticcomposite interfaces.

Carbon Particle/Catalyst Magnetic Composites

There now follows a description of an embodiment of the invention whichincludes the incorporation of carbon particles in association with acatalyst in the cathode interface, and the effects thereof onenhancement of oxygen reduction. An example of a catalyst which may beused in this context is platinum. However, other catalysts that can beemployed include palladium, ruthenium, and rhodium, as well as othertransition metals including cobalt and nickel. Other species could alsocatalyze the reaction such as porphyrins.

It is known that power generation by hydrogen oxygen fuel cells islimited by poor kinetics for oxygen reduction at the cathode. Usually,the oxygen feed is pressurized to shift the reduction of oxygen towardproduct formation, water. As discussed above, the incorporation ofmagnetic material into the cathode of a fuel cell represents a means ofpassive pressurization of oxygen, because oxygen is paramagnetic(susceptible to a magnetic field) and is moved into the cathodeinterface by the presence of the magnetic material. In a refinement ofthe invention, platinized carbon particles, as well as magneticparticles or microbeads, may be incorporated into the cathode interface,as described in more detail below.

Studies of oxygen reduction have shown that the cyclic voltammetriccurrent is enhanced in the presence of magnetic microbeads incorporatedat the cathode interface. The current at the magnetically modifiedelectrodes is about five times as large as the current at electrodesmodified with only an ion exchange polymer such as Nafion. Enhancementsincrease with volume fraction of magnetic beads. The oxygen enhancementis observed when carbon containing a platinum catalyst is included alongwith the magnetic beads and the Nafion.

Thus, according to one embodiment of the invention, a cathode interfacefor oxygen reduction may be optimized by incorporating a magneticcomposite material comprising magnetic particles or microbeads, an ionexchange polymer (e.g. Nafion), and platinized carbon particles, intothe cathode interface. This may impact the performance of fuel cells intwo ways. First, the cathode is pressurized to increase theconcentration of oxygen in the cathode interface. This increasesreactant concentration which, by Le Chatelier's principle, should shiftthe reduction toward products. In an ambient air feed this also helps todisplace the nitrogen gas which builds up in the cathode as the oxygenis depleted from air and the unreactive nitrogen is left behind. Second,one of the loss mechanisms for the oxygen reduction is partial reductionto peroxide (H₂O₂), which then desorbes from the electrode surfacebefore completing its reduction to water. The scheme is as shown below.

The H₂O₂ includes both H₂O₂ (absorbed) and H₂O₂ (solution). The loss ofperoxide to solution may be diminished through the paramagneticproperties of the species on either side of H₂O₂ (adsorbed) in thereaction scheme. If magnetic fields stabilize HO₂ and drive the adsorbedperoxide to dissociate on the surface to form 2 adsorbed paramagneticHO's, then the lifetime of adsorbed H₂O₂ will be decreased and so shouldthe loss through desorption to H₂O₂ (solution). The net effect istherefore an increase in the final step in the reaction scheme, i.e.reduction to water. Cyclic voltammetric results for oxygen reductionusing an electrode having both magnetic microbeads and platinized carbonparticles incorporated into the electrode interface are discussedhereinbelow with reference to FIG. 21.

PEM Fuel Cell Design

Another revolutionary aspect of an ambient pressure PEM fuel cell is theopportunities that it opens up in packaging design. Currently, PEM fuelcells must be encased within a rigid structure in order to contain thepressure applied to the cathode side of the fuel cell. But, the ambientpressure fuel cell increases the flux of oxygen without an externalpressurization requirement. This means that the rigid outer encasementis no longer needed.

PEM fuel cells are inherently amenable to being flexible. The cellitself consists of an anode and cathode separated by an ion exchanger(usually, but not restricted to, Nafion). A fuel cell with amagnetically modified cathode as discussed above which draws air intothe cathode from the atmosphere without compression could be formed withan outside covering similar to the porous vegetable bags made ofpolyethylene or similar polyalkene or other polymer comprised of ahydrocarbon material. Or the fuel cell could be confined to differentgeometries and volumes, and may be flattened again for use or can beused in the confined geometry. Or the nonpressurized cell could havethin plastic outer surfaces and would be approximately as flexible as anoverhead transparency.

The cell would be thin and flexible, about the size of an 8.5×11 inchpiece of paper. While consuming a very small volume of fuel, this wouldprovide more than enough power to run lap-top or notebook computers withor without color displays. Lap-tops and notebooks are currently designedto run on approximately 30 Watts. The fuel cell could be used to run awide variety of portable electronic devices, such as voice and messagecommunications, GPS devices, navigation systems, cameras, etc. A fuelcell with no mechanical pumps, able to sustain good cathode performancecould replace batteries in many systems where small, light-weight,flexible, adaptive power sources are needed.

Another possible embodiment of fuel cells could involve forming an arrayof fuel cells. For example with reference to FIG. 16E, in a single sheet1210 of fuel cells 1220, one of the advantages is that single sheet 1210can contain several fuel cells 1220 thereon. By configuring fuel cells1220 in different serial 1200A and parallel 1200B arrangements (see FIG.16E), fuel cell sheet 1210 can be used to meet a wide variety ofdifferent power demands. For example, single fuel cell sheet 1210 cansubstitute for a wide range of different batteries. If single sheet 1210were divided into, for example, 9 small cells of 1 Volt and 25 Ampseach, the cells can be connected in different ways. If the nine cellsare connected in series, the system will produce 9 Volts and 25 Amps; ifthe cells are connected in parallel, they will produce 1 Volt and 225Amps; and if the cells are connected as a series connection of threesets of three cells in parallel, they will produce 3 Volts and 75 Amps.

Oxygen Concentrators

Another possible application of magnetically modified electrodes orcathodes involving flux enhancement of oxygen relates to the moregeneral problem of concentrating oxygen from the air. The concentrationof oxygen in this case amounts to separating oxygen from nitrogen. Thisproblem may be solved using the magnetically modified electrode orcathode technique or other separation techniques discussed above andherein. Currently, the separation of oxygen from air is donecryogenically which is a costly undertaking. In a magnetic membranesystem where the membrane is placed between ambient (−20% oxygen in air)air and an inner vat (or volume), and the oxygen is immediately sweptfrom the inner vat, a concentration gradient of oxygen is establishedacross the membrane, and oxygen is preferentially drawn into the innervolume from the ambient air.

Membrane Sensors

Membrane sensors for the paramagnetic gases O₂, NO₂, and NO (recentlyidentified as a neurotransmitter) could be based on magnetic compositeswhere enhanced flux would reduce response times and amplify signals.Sensors for other analytes, where oxygen is an interferant, coulddistinguish between species by using dual sensors, identical except onesensor incorporates a magnetic field. Examples of these sensors could beoptical, gravimetric, or electrochemical, including amperometric andvoltammetric. In sensors, the measured signal is proportional to thetotal concentration of all species present to which the sensor responds.The presence of a magnetic component in the sensor will enhancesensitivity to paramagnetic species. Through a linear combination of thesignal from two sensors, similar in all respects except one contains amagnetic component, and the sensitivity of the magnetic sensor toparamagnetic species (determined by calibration), it is possible todetermine the concentration of the paramagnetic species. In a systemwhere the sensors are only sensitive to one paramagnetic and onediamagnetic species, it is possible to determine the concentration ofboth species.

Flux Switches

As nanostructured and microstructured materials and machines developinto a technology centered on dynamics in micro-environments, fluxswitches will be needed. Externally applied magnetic fields can actuateflux switches using electrodes coated with composites made ofparamagnetic polymers and Fe/Fe oxide or Fe particles or othernon-permanent magnetic material, or internal magnetic fields can actuateflux switches using electrodes coated with composites made ofelectro-active polymers or liquid crystals, where one redox form isdiamagnetic and the other is paramagnetic, and organo-Fe or othersuperparamagnetic or ferrofluid materials or permanent magnetic oraligned surface magnetic field material. Also, an external magnet can beused to orient paramagnetic polymers and liquid crystals in a compositecontaining paramagnetic magnetic beads. Enhanced orientation may bepossible with magnetic beads containing superparamagnetic or ferrofluidmaterials.

As discussed above, flux switches may be important components of thesmall scrubber embodiment of the invention described above. They may beimportant for delivery of drugs, biomaterials or medical dosing in aliving organism, where an external or internal magnetic field may turnon/off a flux switch to enable delivery of drugs or biomaterials. Fluxswitches may also be important in imaging applications as alreadydiscussed.

As an extension of the concept of passive oxygen pressurization of fuelcell cathodes, the more general problem of concentration of oxygen fromthe air may be similarly solved. Currently, this is done cryogenicallywhich is a costly undertaking. Essentially, the process of oxygenconcentration according to one embodiment of the invention involves theseparation of O₂ from N₂ using the magnetically modified electrode andseparation techniques described above.

Batteries

Batteries with increased current densities and power, as well asdecreased charge and discharge times may be made with magnetic beadcomposites. The improvements would be driven by flux enhancement,transport enhancement, electron kinetic effects, or by capitalizing on apotential shift. The required mass of microbeads would little affectspecific power. Since magnetic fields can suppress dendrite formation,secondary battery cycle life may be extended. (Note that suppression ofdendrite formation may also be important in plating dense films oflanthanides and actinides.)

The main mechanism of failure for rechargeable batteries is theformation of dendrites. Dendrites are conducting deposits that build-upbetween the two electrodes in the battery during cycling which willeventually short out the cell. It has been shown in tests that anexternally applied magnetic field can suppress dendrite formation.

Therefore, an improved battery may include magnetically modified orcoated electrodes that prevent or suppress dendrite formation. Themagnetic coatings may be on the electrodes or elsewhere in the batterystructure. As discussed above, a magnetic field can be establisheddirectly at the electrode surface by modifying the electrode surfacewith a composite of ion exchanger (polymeric separator) and magneticparticles, eliminating the need for a large external electromagnet toprovide the necessary magnetic field (although in certain circumstancesan externally applied magnetic field may be desirable or useful).Modifying the electrode produces a negligible increase in cell weight(<1%). Also, the flux of ions and molecules through these composites isenhanced substantially compared to the flux through the separator alone.

Using magnetic composites in rechargeable battery systems, threepotential and significant improvements in battery performance areanticipated:

1. Cycle life will be enhanced because of the suppression of dendriteformation by the magnetic field at the surface of the electrodes;

2. Recharge time will be decreased (recharge rate increased) by as muchas ten-fold due to the flux enhancements; and

3. Transient power output will be higher by as much as ten-fold and thedischarge of power will be more rapid due to the flux enhancements.

The charging time is decreased and the transient power is increased tothe extent that the motion of ions and molecules in the cell limitsperformance. A ten-fold (and possibly higher in some cases) enhancementin ion and molecule motion has already been demonstrated in the magneticcomposites.

In a protracted use situation, the cycle life of a battery will beimportant. Cycle life will be enhanced by establishing a magnetic fieldat the electrode surface. As cycle life has not been tested with thecomposites of the type already discussed, it is not yet clear how muchit would be improved. However, a few-fold improvement in cycle life islikely.

The technological advantages that will be seen include:

1. A negligible increase in size and weight (<1%), approximately 5-6lbs;

2. The simplicity of modifying and the compatibility with existingbattery technology; and

3. An insignificant cost of materials to change current batterytechnology (a few cents per battery).

The electrode modification should be useful in a wide variety of batterytypes, including zinc and copper batteries. In these battery types anexternally applied magnetic field has demonstrated suppression of zincand copper deposit dendrite formation.

To demonstrate the suppression of dendrite formation, an electrode mustfirst be modified with a magnetic composite. Once the electrode isavailable, dendrite formation suppression is tested with the electrodein solution. Such tests provide a ready method for examining thefeasibility of magnetic composites in a wide variety of battery systems.

Tests are then performed to test the magnetic composites in a twoelectrode battery system. The fraction of the magnetic particles neededis optimized and the depth of the separator that should contain magneticparticles is determined. Then an evaluation of cycle life, chargingtime, discharging time, power transients, weight change, size change,and cost is made for comparison with a system containing no magneticparticles. Once a cell is constructed using magnetically modifiedelectrodes that shows improvements in cycle life, charging time, andpower transients, the long term stability of the cell is an issue thatmust also be evaluated.

The process just described can be used to create a battery that islight-weight, more efficient, and a longer lasting power source thanconventional batteries with unmodified electrodes. This, coupled with agreatly increased power output, will allow the operation of apparatusrequiring battery power for extended periods of time. Also, moreequipment may be operated with this battery at one time than with aconventional battery.

Methods of Making the Electrode

FIG. 17 is a short summary of steps involved in a method of making anelectrode according to two embodiments of the invention. In oneembodiment, the method is a method of making an electrode with a surfacecoated with a magnetic composite with a plurality of boundary regionswith magnetic gradients having paths to the surface of the electrodeaccording to one embodiment of the invention. In particular step 702involves mixing a first component which includes a suspension of atleast approximately 1 percent by weight of inert polymer coated magneticmicrobeads containing between approximately 10 percent and approximately90 percent magnetizable material having diameters at least about 0.5 μmin a first solvent with a second component comprising at leastapproximately 2 percent by weight of an ion exchange polymer in a secondsolvent to yield a mixed suspension. Step 708 then involves applying themixed suspension to the surface of the electrode. The electrode isarranged in a magnetic field of at least approximately 0.05 Tesla,wherein the magnetic field has a component oriented approximately alongthe normal of the electrode surface and preferably is entirely orientedapproximately along the normal of the electrode surface. Step 714 theninvolves evaporating the first solvent and the second solvent to yieldthe electrode with a surface coated with the magnetic composite having aplurality of boundary regions with magnetic gradients having paths tothe surface of the electrode.

Step 702 can include mixing the first component which includes asuspension of between approximately 2 percent and approximately 10percent by weight of inert polymer coated magnetic microbeads with thesecond component. Alternatively, step 702 can include mixing the firstcomponent which includes inert polymer coated magnetic microbeadscontaining between 50 percent and 90 percent magnetizable material withthe second component. Alternatively, step 702 can include mixing thefirst component which includes inert polymer coated magnetic microbeadscontaining 90 percent magnetizable material with the second component.

In addition, step 702 can include mixing a first component whichincludes a suspension of at least approximately 5 percent by weight ofinert polymer coated magnetic microbeads containing betweenapproximately 10 percent and approximately 90 percent magnetizablematerial having diameters ranging between approximately 0.5 μm andapproximately 12 μm with a second component. Alternatively, step 702 caninclude mixing a first component which includes a suspension of at leastapproximately 5 percent by weight of inert polymer coated magneticmicrobeads containing between approximately 10 percent and approximately90 percent magnetizable material having diameters ranging betweenapproximately 0.1 μm and approximately 2 μm with a second component.

Mixing step 702 can also involve mixing a first component which includesa suspension of at least approximately 5 percent by weight of inertpolymer coated magnetic microbeads containing between approximately 10percent and approximately 90 percent magnetizable material havingdiameters at least 0.5 μm in a first solvent with a second componentcomprising at least approximately 5 percent by weight of Nafion in asecond solvent to yield the mixed suspension.

Step 702 can involve mixing a first component which includes asuspension of at least approximately 5 percent by weight of inertpolymer coated magnetic microbeads containing between approximately 10percent and approximately 90 percent organo-Fe material having diametersat least 0.5 μm in a first solvent with a second component comprising atleast approximately 5 percent by weight of an ion exchange polymer in asecond solvent to yield the mixed suspension.

Step 708 can include applying approximately between 2 percent andapproximately 75 percent by volume of the mixed suspension to thesurface of the electrode. Alternatively, step 708 can include applyingbetween 25 percent and 60 percent by volume of the mixed suspension tothe surface of the electrode. In yet another approach step 708 caninvolve applying the mixed suspension to the surface of the electrode,the electrode being arranged in a magnetic field between approximately0.05 Tesla and approximately 2 Tesla and preferably the magnetic fieldis approximately 2 Tesla.

An alternative embodiment involving steps 702′ through 714′ (also shownin FIG. 17) involves the use of an external magnetic field. That is,again the method of making an electrode with a surface coated with acomposite with a plurality of boundary regions with magnetic gradientshaving paths to the surface of the electrode when the external magneticfield is turned on. The steps 702 through 714 are then modified intosteps 702′ through 714′ as follows. Step 702′ involves mixing a firstcomponent which includes a suspension of at least 5 percent by weight ofinert polymer coated microbeads containing between 10 percent and 90percent magnetizable non-permanent magnetic material having diameters atleast 0.5 μm in a first solvent with a second component comprising atleast 5 percent of an ion exchange polymer in a second solvent to yielda mixed suspension. Step 708′ then involves applying the mixedsuspension to the surface of the electrode. Step 714′ involvesevaporating the first solvent and the second solvent to yield theelectrode with a surface coated with the composite having a plurality ofboundary regions with magnetic gradients having paths to the surface ofthe electrode when the external magnet is turned on.

A method for making a composite comprising carbon particles inassociation with a catalyst, such as platinum, and which is tailored toenhancing oxygen reduction current at an electrode, is outlined below.In general, this protocol is similar to that outlined above withreference to FIG. 17, with the exception that carbon particles with somedegree of loading of a catalyst, for example, platinum, are included inthe casting mixture. Briefly, the procedure is as follows:

Step 1) A casting mixture is formed comprising the following components:

i. a suspension of an ion exchange polymer, such as Nafion,

ii. magnetic particles or microbeads, which may be coated to render theminert,

iii. carbon particles in association with a catalyst, typicallyplatinum. Other examples of catalysts were provided above.

iv. at least one casting solvent

Depending, among other factors, on the particular application orintended use, magnetic composites may be formed according to theprocedure outlined above wherein the composite comprises from about 85%to about 0.01% by weight of magnetic material, and from about 15% toabout 99.99% by weight of an ion exchange polymer. The magnetic materialcomponent in the casting mixture which is used to make-up the compositemay be in the form of magnetic particles, beads or microbeads of ironoxides (e.g. Fe₂O₃, Fe₃O₄) or of other magnetic materials, and may becoated or non-coated (encapsulated or non-encapsulated).

The amount of catalyst present in association with the carbon particlesmay be varied over a fairly broad range, according to, among otherthings, other parameters associated with formulation of the castingmixture, for example the percentages of Nafion, carbon particles, andmagnetic microbeads present in the casting mixture. The amount ofcatalyst present in association with the carbon particles may range, forexample, from about 5% (by weight) to about 99.99% (by weight) of thecombined weight of the carbon particles plus catalyst. In the case ofplatinum comprising the catalyst in association with the carbonparticles, the platinum may be present primarily or solely on thesurface of the carbon particles. (Alternatively, platinum can be used ascatalyst and conductor instead of the carbon. The amount of the carbonparticles in association with a catalyst component of a magneticcomposite may range from 0.01% to about 80% by weight (or mass) of thetotal weight of the magnetic composite.

Another variable in formulating the casting mixture and in the method ofmaking the electrode is the size and type of the carbon particles.Preferably, the carbon particles are in the range of 15 μm to 70 μm. Itshould also be noted that, according to another embodiment of theinvention, particles containing platinum could be used as a component ofthe magnetic composite, either in lieu of, or in addition to, the carbonparticles in association with a catalyst component. Such particlescontaining platinum may lack a carbon constituent, or may be composedpredominantly or solely of platinum (i.e. up to 100% platinum). In thelatter case the particles composed predominantly or solely of platinummay function as a catalyst and/or as electron conductors, and may servea dual role as both catalyst and electron conductors. The particles acontaining platinum component of the composite may comprise as little asabout 0.1% of platinum by weight. The particles containing platinumcomponent of the composite may also consist essentially of platinum withtrace amounts of other materials, such as carbon (e.g. 99.99% platinumand 0.01% carbon). Thus there may be a continuum between carbonparticles in association with a catalyst, wherein the catalyst isplatinum, and particles containing platinum, wherein the particlescontaining platinum comprise carbon. (Increasing the platinum content ofa composite would likely result in increased cost of materials used inits manufacture.)

Step 2) The casting mixture is thoroughly agitated, for example bysonication or stirring with a mechanical stirring device, and an aliquotis transferred to the electrode surface. The electrode serves as acurrent collector. At this stage, before the casting solvent(s)evaporate, the electrode may be placed in a magnetic field. Such amagnetic field orients the magnetic particles and gives rise to anordered structure. (There is some evidence that an external magneticfield is unnecessary.)

Step 3) The external magnet, if any, is removed leaving behind amagnetic composite on the current collector.

Step 4) The modified electrode may now be placed in a matrix, e.g. insolution, where oxygen is fed to the current collector through themagnetic composite from the solution or other matrix.

FIGS. 18A and 18B show a flux switch 800 to regulate the flow of a redoxspecies according to yet another embodiment of the invention. Inparticular, FIGS. 18A and 18B show an electrode 804 and a coating 808 onthe electrode 804. Coating 808 is formed from a composite which includesmagnetic microbead material 812 with an aligned surface magnetic field;an ion exchange polymer 816; and an electro-active polymer 820 in whicha first redox form is paramagnetic and a second redox form isdiamagnetic, wherein the flux switch is actuated by electrolyzing theelectro-active polymer from the first redox form ordered in the magneticfield established by the coating to the second redox form disordered inthe magnetic field.

Microbead material 812 can include organo-Fe material. The redox speciescan be more readily electrolyzed than the electro-active polymer.Electro-active polymer 820 can be an electro-active liquid crystal withchemical properties susceptible to said magnetic field or anelectro-active liquid crystal with viscosity susceptible to saidmagnetic field. Electro-active polymer 820 includes an electro-activeliquid crystal with phase susceptibility to said magnetic field.Electro-active polymer 812 can include polyvinyl ferrocenium). Inaddition, magnetic particles or microbeads can comprise organo-Fematerial.

FIG. 19 shows a dual sensor 900 for distinguishing between a firstspecies (particles A) and a second species (particles B). The dualsensor includes a first membrane sensor 906 which preferentially passesthe first species over the second species; and a second membrane sensor912, which preferentially enhances the concentration of the secondspecies over the first species, thereby enabling the measurement of atleast the first species. The first and second species can be in anystate such as liquid, gaseous, solid and plasma.

In one embodiment of the dual sensor, the first species can include aparamagnetic species and the second species can include a diamagneticspecies. In this case, the first membrane sensor 906 is a magneticallymodified membrane sensor, and the second membrane sensor 912 is anunmodified membrane sensor. The magnetically modified membrane sensorpreferentially enhances the concentration of and allows the detection ofthe paramagnetic species over the diamagnetic species and the unmodifiedmembrane sensor enhances the concentration of and allows the detectionof the diamagnetic species and the paramagnetic species, enabling themeasurement of the concentration of at least the paramagnetic species.More particularly, the paramagnetic species can be one of O₂, NO₂, andNO. The diamagnetic species can be CO₂.

In another embodiment, the first species can include a paramagneticspecies and the second species can include a nonmagnetic species. Inthis case, the first membrane sensor 906 is a magnetically modifiedmembrane sensor, and the second membrane sensor includes an unmodifiedmembrane sensor. The magnetically modified membrane sensorpreferentially enhances the concentration of and allows the detection ofthe paramagnetic species over the nonmagnetic species and the unmodifiedmembrane sensor enhances the concentration of and allows the detectionof the nonmagnetic species and the paramagnetic species, therebyenabling the measurement of the concentration of at least theparamagnetic species. More particularly, the paramagnetic species can beone of O₂, NO₂, and NO.

In yet another embodiment, the first species can include a diamagneticspecies and the second species can include a second diamagnetic species.In this case, first membrane sensor 906 is a magnetically modifiedmembrane sensor, and second membrane sensor 912 is a differentlymagnetically modified membrane sensor. The magnetically modifiedmembrane sensor preferentially enhances the concentration of and allowsthe detection of the first diamagnetic species over the seconddiamagnetic species and the differently magnetically modified membranesensor enhances the concentration of and allows the detection of thesecond paramagnetic species and the diamagnetic species, enabling themeasurement of the concentration of at least the first diamagneticspecies. The first diamagnetic species can include CO₂.

In yet another embodiment, the first species can be a first paramagneticspecies and the second species can be a second paramagnetic species. Inthis case, first membrane sensor 906 is a magnetically modified membranesensor, and second membrane sensor 912 is a differently magneticallymodified membrane sensor, wherein the magnetically modified membranesensor preferentially enhances the concentration of and allows thedetection of the first paramagnetic species over the second paramagneticspecies and the differently magnetically modified membrane sensorenhances the concentration of and allows the detection of the secondparamagnetic species and the first paramagnetic species, enabling themeasurement of the concentration of at least the first paramagneticspecies. Again, the first paramagnetic species can be one of O₂, NO₂,and NO.

In yet another embodiment of the invention, the first species can be adiamagnetic species and the second species can be a nonmagnetic species.In this case, first membrane sensor 906 is a magnetically modifiedmembrane sensor, and second membrane sensor 912 is an unmodifiedmembrane sensor, wherein the magnetically modified membrane sensorpreferentially enhances the concentration of and allows the detection ofthe diamagnetic species over the nonmagnetic species and the unmodifiedmembrane sensor enhances the concentration of and allows the detectionof the nonmagnetic species and the diamagnetic species, enabling themeasurement of the concentration of at least the diamagnetic species.

FIG. 20 shows a cell 201 according to another embodiment of theinvention. In particular, FIG. 20 shows an electrolyte 205 including afirst type of particles. A first electrode 210 and a second electrode215 are arranged in electrolyte 205. The first type of particlestransform into a second type of particles once said first type ofparticles reach said second electrode 215. Second electrode 215 has asurface with a coating 225 fabricated according to the above methods.Coating 225 includes a first material 230 having a first magnetism, anda second material 234 having a second magnetism, thereby creating aplurality of boundaries (33 of FIG. 15A) providing a path betweenelectrolyte 205 and said surface of second electrode 215. Each of saidplurality of boundaries having a magnetic gradient within said path,said path having an average width of approximately one nanometer toapproximately several micrometers, wherein said first type of particleshave a first magnetic susceptibility and said second type of particleshave a second magnetic susceptibility and the first and said secondmagnetic susceptibilities are different. Coating 225 operates in themanner described with respect to FIG. 16.

First material 230 in coating 225 can include a paramagnetic species andsecond material 234 can include a diamagnetic species. Alternatively,first material 230 can include a paramagnetic species having a firstmagnetic susceptibility and second material 234 can include aparamagnetic species having a second magnetic susceptibility, whereinsaid first magnetic susceptibility is different from said secondmagnetic susceptibility. In yet another approach, first material 230 caninclude a diamagnetic species having a first magnetic susceptibilitywhile second material 234 includes a diamagnetic species having a secondmagnetic susceptibility, and said first magnetic susceptibility isdifferent from said second magnetic susceptibility. In another approach,first material 230 could alternatively include a paramagnetic specieshaving a first magnetic susceptibility and second material 234 comprisesa nonmagnetic species. In another approach, first material 230 caninclude a diamagnetic species having a first magnetic susceptibility andsecond material 234 can include a nonmagnetic species. Electrolyte 205can be an electrolyzable gas such as O₂ or can include a chlor-alkali.

Chromatographic Flux Enhancement by Nonuniform Magnetic Fields

Using a chromatographic approach, as discussed above, flux may beenhanced by nonuniform magnetic fields. This is a separation orchromatographic application (magnetochromatography) and it involves noelectrochemistry. The basis of the invention follows.

The basic methodology comprises taking an iron (or other magnetizablematerial) wire and coating it to make it chemically inert. The iron wireis threaded inside a capillary. The capillary is filled with a polymer,or gel, or other material through which molecules and/or ions can move.Alternatively, the polymer or other material can be dip coated or castdirectly on the surface of the inert coating; this eliminates the needfor the capillary. The ions and/or molecules to be separated areintroduced into one end of the capillary. A gradient is establishedalong the length of the tube to cause motion of the molecules and/orions through the tube. The gradient could be, for example, aconcentration or a potential gradient. (There are a whole range ofgradients used in chromatography that can be directly drafted into thissystem. Besides concentration and potential gradients, these includegradients of density, viscosity, pressure, temperature, ion exchangecapacity, characteristic dimensions of the microstructured substrate(stationary phase) polarity and dielectric constant, as well as forcedflow and convection, and time dependency (temporal gradients andpulses)). The capillary is placed inside a magnetic field. A circularmagnet could be used, but other geometries are possible. The magneticfield will be concentrated inside the iron wire, and as the field decaysinto the polymer or gel surrounding the wire, a nonuniform magneticfield will be established. Moieties moving through the gel will be drawntoward the wire and swept down the tube by the concentration gradientand surface diffusion processes.

Variations in specific embodiments are possible. A wire is discussedabove, but any shape including beads will work. The wire can be anymagnetizable material such as iron or iron oxides, as well as permanentmagnets and superconductors.

The coating on the wire to make it chemically inert could includepolymers, silanes, thiols, silica, glass, etc. In some systems, thechoice of wire, solvent and substrate may create a system where the“wire” is already inert and no coating is needed.

The polymer or gel in the capillary can be one of the ion exchangepolymers already discussed (Nafion and poly(styrene sulfonate)) or othermaterial, probably having a viscosity higher than that of bulk solvent.Other examples could involve separation materials commonly used inchromatography—including acrylamide polymers, acrylate polymers, Dow-Ex(Trademark of Dow-Corning Corporation) materials, or maybe just sucroseor glycerol (glycerin) in solvent.

Ions and/or molecules can be introduced from any phase (gas, liquid,solid, or plasma), although liquid is the most obvious. Molecules can beintroduced continuously for a continuous separation or in single shotsor in a series of shots. The nonmagnetic gradient is needed to pullmolecules that move into the surface zone rapidly down the tube so moremolecules can be drawn in by the magnetic field.

The concentration of the field inside a magnetizable wire or otherstructure by the external magnet can be controlled with pulsed fields,reversed fields, DC fields, and graded fields as only some examples ofwhat can be done to control the separation and transport direction(vector) of the materials. A combination of different magnetizablematerials inside the gel—either parallel or crossed, might provide someinteresting mechanisms for vectoring molecules or ions and separatingthem according to differences in their susceptibilities. Note, thecombination of vectors provides a mechanism for separations of alltypes.

Note also that the switching possibilities here are significant. Byusing an external electromagnet in this system, it should be possible toturn the effect on and off. If superconductors are used, the switchingcan be done by turning the field on and off by temperature changes.

All the existing separation methodologies of chromatography andseparation science can be brought to bear here. Separations are drivenby various gradients and flows. These include diffusion, migration,fluid flow, size exclusion, thermal programming, electrophoresis,electro-osmosis, etc.

An embodiment of the above discussed chromatographic technique is shownin FIG. 20A. FIG. 20A shows apparatus 1100 comprising capillary 1110,magnets 1120, iron wire 1130, polymer gel 1140, solvent 1150, andspecies 1160. FIG. 20B shows rough magnetic field lines that may beconcentrated in iron wire 1130. Species 1160 is to be separated fromother species introduced through one end of capillary 1110. Species 1160is fed into one end of capillary or tube 1110 containing solvent 1150and caused to move through capillary or tube 1110 driven by a gradient(concentration, potential, or other gradient) and is subsequently passedthrough or is swept down capillary 1110 or through polymer gel 1140therein, wherein movement of species 1160 is influenced by its ownmagnetic properties (magnetic susceptibility) and the magnetic fieldconcentrated in iron wire 1130 by magnets 1120. Thereafter, species 1160is collected after passing through the other end of capillary or tube1110 and separated from other species not passing through capillary1110.

A method comprising steps for this chromatographic process may bedescribed in FIG. 20C as follows. In step 1170 an iron wire is coated tomake it chemically inert. The iron wire is then threaded inside acapillary or tube in step 1172A. A capillary is filled with a polymer,gel, or other material (which may be viscous) through which moleculesand/or ions can move in step 1172B. Alternatively, the inert wire is dipcoated or cast with a polymer, gel, or other material (may be viscous)directly in step 1173. The inert wire is placed inside a magnetic fieldin step 1176 with or without the capillary, depending on the previousalternative steps. A gradient is established along the length of thetube to carry the mobile species (including species to be separated)down the tube in step 1178. Species with the highest magneticsusceptibilities (including the species to be separated) are pulled intothe interface between the inert coating and the polymer, gel, or othermaterial (viscous matrix), the facile transport zone of the interfacewhich enhances the flux of the magnetically susceptible species in step1180. In step 1180, species move through the interface between polymeror other materials and the inert coating through which molecules and/orions can move and are swept down the tube by the gradient and surfacediffusion processes according to the magnetic properties of the species,the magnetic field concentrated in the iron wire, and the magneticgradient established in the system from the iron wire and the externalfield.

Another method that could be followed for the apparatus involves:placing an iron wire (or other material) into a heat shrink material instep 1310, perhaps teflon; heat shrinking the heat shrink material instep 1320; dip coating with a layer of Nafion or PSS; drying thedip-coated layer, perhaps in a vacuum desiccator in step 1330; cappingthe ends of the coated wire and sliding the coated wire into tubing,perhaps spaghetti tubing in step 1340; placing one end of the tubing ina solution that contains the species to be separated in step 1350;placing the other end of the tubing into a solution that does notcontain the species to be separated (this sets up a concentrationgradient down the length of the tubing) in step 1360; placing the entiresystem in a magnetic field that is oriented radially with respect to theiron wire, perhaps in a hollow cylindrical magnet in step 1370. Thisprocess will enhance the separation of paramagnetic species. Note thatthe wire may be made of material other than iron, such as permanentmagnets. The wire may also be in different geometries than a typicalwire, such as a plate, disk, or any other shape or volume.

FIG. 21 shows cyclic voltammetric results for oxygen reduction using anelectrode having both magnetic particles or microbeads and platinizedcarbon particles incorporated into the electrode interface, as describedabove. Oxygen reduction was compared for electrodes having fourdifferent types of surface modifications, as detailed below. In theexperiment, the solution was saturated with oxygen, and then thepotential applied to the electrode was scanned at 500 mV/s from apotential where no oxygen reduction occurs (+800 mV) to a potentialwhere all the oxygen in the vicinity of the electrode surface iselectrolyzed (−200 mV). Curve number 1 of FIG. 21 shows data for asimple film of Nafion on the electrode surface (i.e. 100% Nafion).Slightly higher currents are observed for films containing 43% Nafionand 57% platinized carbon (curve No. 2) and 33% Nafion, 11% nonmagneticpolystyrene beads, and 56% platinized carbon (curve No. 3) (allpercentages by volume). Curve No. 4 shows data for a film of 32% Nafion,11% magnetic polystyrene beads, and 57% platinized carbon (allpercentages by volume). Note that for the magnetic composite the currentfor oxygen reduction (at about 250 mV vs SCE (a reference electrode)) issignificantly higher. The concentration of platinum of the platinizedcarbon was 40% by weight in each case. These results are not optimized,but indicate that the incorporation of magnetic particles and platinizedcarbon into the electrode interface significantly enhances the oxygenflux under transient voltammetric conditions.

The data presented above further substantiate the claim that amagnetically modified interface has a significant impact in enhancingthe current and flux of oxygen. This enhancement can be driven by threemechanisms. First, the flux of oxygen may be increased by the magneticfields. Second, the magnetic fields may impact the oxygen reductionkinetics. Third, the magnetic columns or particles may serve to betterdistribute the platinized carbon throughout the composite and so enhancecurrent collection efficiency, either by distributing thecatalyst/carbon electron conductor more uniformly throughout theinterface and/or increasing the surface area where oxygen is adsorbedand awaiting reduction.

In FIG. 22, kD^(1/2)C⁺, a parameter proportional to the peak cyclicvoltammetric current, is plotted on the y-axis, while the carbon masspercent (or % by weight) in the composite was varied over the range of10% to 50% (i.e. from 10 g to 50 g of carbon particles in associationwith a catalyst per 100 g of composite). The magnetic bead fraction washeld constant at 10% (mass percent or % by weight) in these studies. Theremaining fraction of the composite is Nafion. The platinumconcentration of the platinized carbon was 10, 20, 30 or 40% by weight.Each point represents a single experiment. The flux enhancement isgreater for 30% and 40% platinum on carbon than for 20% or 10%.Essentially, at the higher concentrations of platinum, additionalcatalyst does not enhance the flux.

The comparisons of the different film composites in FIG. 21 clearlyindicate that the flux is higher in a magnetic environment, but theresults do not definitively identify the flux enhancement as due to amagnetic effect. The structure of the magnetic composites is differentfrom the structure of the nonmagnetic composites. The results do notrule out increased surface area as the only source of the fluxenhancement.

Table 4 shows measured values of the parameter kD^(1/2)C for a varietyof different experiments. In the experiments, an electrode used wasmodified with Nafion, Nafion and nonmagnetic beads, or Nafion andmagnetic beads. The relative peak current is a measure of theenhancement in the oxygen reduction signal, and is listed as kD^(1/2)Cwhere k is the extraction parameter, D is the diffusion coefficient ofO₂ in the film, and C is the concentration of the oxygen in solution.The parameter kD^(1/2)C is determined from the slope of a plot of thepeak currents versus square root of scan rate. The slope is renormalizedby the electrode area, Faraday's constant (96485 coulombs/mole ofelectrons) and number of electrons transferred (approximated as 4). Theexperiments in Table 4 are grouped by the dates they were performed.Since there is no good way to determine the oxygen content at the timethese studies were performed, it is best to compare the results for agiven day, and hence it is best to compare results within a given group.The Nafion film and bare electrode data can serve as a rough estimate ofthe oxygen content. In the group marked A, no carbon is included in theinterface, and there is no evidence that the magnetic particles enhancethe reduction of oxygen. In the rest of the samples, carbon is includedin the matrix on the electrode. In general, the results indicate thatwhen carbon is included on the electrode, the electrolysis current isenhanced in the presence of the magnets. Also, it should be noted thatthese enhancements are larger when the magnetic content is increased.

Electrode Surface Modification to Prevent Passivation and Enable DirectReformation of Fuels

A major constraint to fuel cell development and design is the problem ofelectrode passivation, which results from the reaction of electrolyticintermediates with the electrode surface, and effectively terminates ordrastically impedes the electrolytic process. The available evidenceindicates that electrode passivation (which occurs rapidly) is directlyresponsible for the failure of prior art fuel cells to utilize theprocess of direct reformation. Direct reformation is a process wherein afuel, such as a liquid alcohol fuel (e.g. methanol, ethanol) or ahydrocarbon fuel (e.g. propane) is delivered directly to an electrode(the anode), where it is oxidized (reformed) directly. During directreformation, in a fuel cell or other setting, a liquid or gaseous fuelmay be transported from a suitable source of fuel or fuel storage deviceand delivered to the appropriate electrode(s) via one or more deliveringmeans, which may include various suction and pressurization devices,including various types of pumps. Devices for moving and/or deliveringliquids and gases, including fuels, including pumping devices, are wellknown in the art.

Studies of ethanol oxidation show that the cyclic voltammetric currentis enhanced in the case of electrodes modified with a coating ofmagnetic composites comprising magnetic microbeads and carbon particlesin association with a catalyst, as compared with bare (i.e. uncoated)electrodes or electrodes modified with a coating of a composite whichlacks either magnetic microbeads or carbon particles in association witha catalyst. In a preferred embodiment of the invention, the carbonparticles in association with a catalyst comprise particles of carbon inassociation with platinum, i.e. a form of platinized carbon (Pt-C). Thecyclic voltammetric data on ethanol oxidation are presented in FIGS. 23through 29, and collectively indicate not only the feasibility for theprevention of electrode passivation, but also the parameters for thedirect reformation of ethanol at the surface of a magnetically modifiedelectrode.

Magnetic modification of electrodes may be achieved by methods similarto those described above on modification of electrodes with a magneticcomposite in the context of enhancement of the electrochemical reductionof oxygen. For example, a casting mixture may be formulated to include:

1. A suspension of an ion exchange polymer, such as Nafion;

2. Magnetic microbeads or particles, which may be encapsulated or coatedwith an encapsulating material, or non-encapsulated; and

3. At least one suitable solvent or a solvent mixture to serve as avehicle or carrier for components 1 through 3.

Depending on a number of factors, including the particular applicationor intended use of the magnetic composite material, the casting mixturemay further include carbon particles in association with a catalyst,and/or particles containing platinum.

The casting mixture is agitated by, for example, sonication or stirring,and an aliquot of the casting mixture is deposited on the surface of abare or uncoated electrode. The electrode serves as a current collector.

Before the solvent, solvent mixture or carrier has evaporated, theelectrode may be arranged in an external magnetic field in order toorient the magnetic particles and form an ordered structure on thesurface of the electrode (as described in greater detail elsewhereherein). (There is, however, some evidence that the presence of anexternal magnetic field may be optional.)

After the solvent or carrier has evaporated, the external magnet, ifany, is removed to yield a coating of a magnetic composite in surfacecontact with the magnetically modified electrode. The thickness of thecoating or film of the magnetic composite on the electrode surfacedepends on various parameters of the process of electrode modification,such as the volume of casting mixture cast per unit area of electrodesurface. In general, the thickness of the magnetic composite coating isin the range of 0.5 to 100 μm. A preferred range for the thickness ofthe magnetic composite coating is from 2 to 25 μm.

The nature and relative amounts of the various components comprising thecasting mixture, and therefore the composition of the composite coatingor film on the electrode surface, may vary. In general, the compositecoating comprises between about 0.01% and about 85% of beads ormicrobeads, such as magnetic microbeads comprising oxides of iron; andfrom about 15% to about 99.99% of an ion exchange polymer, by weight. Amagnetic composite coating may, optionally, further comprise from 0% toabout 80% by weight of carbon particles in association with a catalyst,and/or particles containing platinum. Typically the catalyst comprisesplatinum, and the catalyst may be loaded on the surface of the carbonparticles. Variables related to the carbon particles in association witha catalyst component include the nature and degree of loading of thecatalyst on the surface of the carbon particles, and the size and typeof the carbon particles. The particles containing platinum may lackcarbon or may include carbon, and may be comprised predominantly ofplatinum, or the particles containing platinum may consist essentiallyof platinum (i.e. having about 95% to about 100% platinum, by weight, ofthe particles containing platinum).

A preferred type of carbon particle comprising a composite material isVulcan XC-72. A catalyst, in association with carbon particles, that canbe employed in practicing the invention may include platinum, palladium,ruthenium, or rhodium, as well as other transition metals includingcobalt and nickel. The amount of catalyst in association with the carbonparticles may range from about 5% or less to about 99.99%, by weight; amore preferred range is from about 10% to about 50% by weight. Apreferred catalyst which may be used in combination with carbonparticles is platinum. In a more preferred embodiment of the invention,the platinum is disposed on the surface of the carbon particles.

A preferred ion exchange polymer comprising a composite coating or film,under the invention, comprises Nafion. The magnetic microbead componentof a magnetic composite may comprise beads of magnetic material, such asiron(III) oxide or magnetite, which may or may not be coated with anencapsulating material. The encapsulating material which may be used toencapsulate or coat the magnetic microbeads may be an inert material. Inone embodiment of the invention an encapsulating material comprisespolystyrene. The percentage by weight of magnetic or magnetizablematerial comprising the magnetic microbead component of the magneticcomposite is normally between 2% and 90%. The size of the magneticparticles, beads or microbeads comprising the magnetic compositematerial range in diameter from about 0.1 micrometer to about 50 μm; andmore preferably the magnetic microbeads are in the range of from 1 to 10μm in diameter.

The range of encapsulating materials which may be used to coat orencapsulate magnetic microbeads under the invention may include, forexample: various polymers, silanes, thiols, silica, glass, etc.

The solvent, solvent mixture or carrier component of the casting mixturemay comprise any suitable solvent, or combination of two or moresolvents, which will suitably dissolve and/or suspend the othercomponents of the casting mixture and allow for the distribution of thecasting mixture on the surface of the electrode.

The surfaces of platinum electrodes were modified by coating theirsurface with a number of different composites comprising an ion exchangepolymer, magnetic microbeads, and carbon particles in association with acatalyst. For comparative purposes, composites were also preparedcomprising an ion exchange polymer in combination with non-magneticmicrobeads, with or without carbon particles in association with acatalyst. Once the composite material coating the modified electrode isdry, the electrode may be placed in a solution or other matrixcontaining a fuel, such as ethanol.

Unmodified (bare) platinum electrodes and the variously modifiedelectrodes were then studied in the context of ethanol oxidation bycyclic voltammetry. The electrodes were removed from the externalmagnetic field before making voltammetric measurements.

In a first series of experiments, electrodes modified with a surfacecoating or film of the ion exchange polymer Nafion and non-magnetic(polystyrene) beads (diameter=1 to 3 μm) were compared with electrodesmodified with a surface coating or film of the ion exchange polymerNafion and magnetic beads (diameter=1 to 3 μm). In each case, thecomposite coating or film consisted of 25% beads and 75% Nafion, byvolume. Films or composite coatings were cast on a polished platinumdisk electrode, having an area of 0.46 cm². The films were then dried ina vacuum desiccator for 1 hour. The electrodes were placed in a solutionof ethanol, with 0.1 M Na₂SO₄ as the electrolyte, in 18 megohm Milli-Qwater. The solution was not purged, but rather was at ambientconditions. After soaking in the solution for 1 hour, each electrode wascycled 100 scans at a scan rate of 500 mV/s between −700 and 900 mVbefore data was recorded. This repeated cycling was performed in orderto allow, or induce, passivation in an electrode which is susceptible topassivation, or which can be passivated by repeated cycling. Cyclicvoltammograms were then recorded at scan rates of 500, 200, 100, 50, and20 mV/s for both the electrode bearing the magnetic film and for thatbearing the non-magnetic film. The results of the first series ofexperiments are shown in FIGS. 23A, 23B, and 24A-C.

FIGS. 23A and 23B show cyclic voltammetric data for ethanol oxidation (6mM ethanol in 0.1 M Na₂SO₄) using a platinum electrode bearing a surfacecomposite comprising Nafion and either non-magnetic microbeads (23A) ormagnetic microbeads (23B) (25% beads, 75% Nafion, by volume). Cyclicvoltammograms were recorded at scan rates of 500, 200, 100, 50, and 20mV/s. FIG. 24A, 24B, and 24C show cyclic voltammetric data for ethanoloxidation (7 mM ethanol in 0.1 M Na₂SO₄) using a platinum electrodebearing a surface composite comprising non-magnetic microbeads andNafion (25% beads, 75% Nafion, by volume), and using a platinumelectrode bearing a surface composite comprising magnetic microbeads andNafion (25% beads, 75% Nafion, by volume). Cyclic voltammograms wererecorded at a scan rate of 500 mV/s (FIG. 24A), 100 mV/s (FIG. 24B), and20 mV/s (FIG. 24C).

When the voltammetry of ethanol electrolysis using the differentlymodified electrodes is compared, little or no difference is discerniblein the case of the magnetic composite coating as compared with thenon-magnetic coating in the absence of platinized carbon. With theexception of the 500 mV/s scan rate, the cyclic voltammograms for themagnetic and non-magnetic films overlaid one another. In FIG. 24A, whichshows data for the 500 mV/s scan rate, the peak between −600 and −200 mVis much larger for the non-magnetic film as compared with the magneticfilm, while the respective second peaks almost overlay one another. InFIGS. 24B and 24C, there is no distinguishable difference between themagnetic and non-magnetic films.

In a second series of experiments concerning the voltammetry of ethanolelectrolysis, electrode surfaces were modified with a compositecomprising carbon particles in association with a platinum catalyst.Thus, electrodes having a coating or film comprising platinized carbonparticles, Nafion, and magnetic beads were compared with electrodeshaving a coating comprising platinized carbon particles, Nafion andnon-magnetic (polystyrene) beads, and with uncoated (bare) electrodes.The experimental details were otherwise generally as outlined above forthe first series of experiments, with the exceptions described below.

Four different composites were formulated to coat the electrodes used inthe second series of experiments, and are designated as Films 6 through9. The carbon particles in association with a catalyst used in thesefilms was in the form of Vulcan XC-72 (E-Tek, Natick, Mass.) containing20% platinum, by weight. This component of the composite coating or filmis referred to as Pt-C. The percentage, by weight, of beads in thedifferent composite formulations used to form each film was keptconstant at 11%. Films 6 and 9 contain non-magnetic, polystyrene, beads,while films 7 and 8 contain magnetic beads. The composition, by weight,of each of the four films is as follows:

Film 6: 26% Pt-C; 63% Nafion; 11% polystyrene beads

Film 7: 26% Pt-C; 63% Nafion; 11% magnetic beads

Film 8: 76% Pt-C; 13% Nafion; 11% magnetic beads

Film 8: 76% Pt-C; 13% Nafion; 11% polystyrene beads

Cyclic voltammograms were taken, at a range of scan rates, forelectrodes coated with one of films 6 through 9, and for a bare(uncoated) electrode. The results are presented in FIGS. 25 through 29.

FIG. 25 shows cyclic voltammetric data for ethanol oxidation (6.852 mMethanol in 0.1003 M Na₂SO₄) using the bare (uncoated) platinumelectrode, recorded at scan rates of 500, 200, 100, 50, and 20 mV/s.FIGS. 26A and 26B show cyclic voltammetric data for ethanol electrolysis(6.852 mM ethanol in 0.1003 M Na₂SO₄) using platinum electrodes bearingthe surface composites designated Films 6 and 7, respectively.Voltammograms were recorded at scan rates of 500, 200, 100, 50, and 20mV/s. FIGS. 27A and 27B show cyclic voltammetric data for ethanolelectrolysis (6.852 mM ethanol in 0.1003 M Na₂SO₄) using platinumelectrodes bearing the surface composites designated Films 8 and 9,respectively. Voltammograms were again recorded at scan rates of 500,200, 100, 50, and 20 mV/s.

FIG. 28A shows cyclic voltammetric data for ethanol oxidation (6 mMethanol in 0.1 M Na₂SO₄) using a bare platinum electrode, and usingplatinum electrodes bearing surface composites designated as Film 6(non-magnetic) or Film 7 (magnetic). The voltammograms were recorded ata scan rate of 500 mV/s. It can be seen that at this scan rate the bareelectrode and the electrode coated with non-magnetic Film 6 haveapproximately the same current. In contrast, the electrode coated withthe magnetic Film 7 shows current at about twice the value recorded forthe electrode coated with the non-magnetic film.

The oxidation of ethanol is a multielectron process, with numerousintermediates; the steps occur over a range of potentials and thepotential is pH dependent. However, the peak at about −100 mV observedfor the magnetic composite film corresponds to ethanol oxidation (seeFIG. 28A). FIGS. 28B and 28C also show cyclic voltammetric data forethanol oxidation (6 mM ethanol in 0.1 M Na₂SO₄) using a bare platinumelectrode, and using platinum electrodes bearing surface compositesdesignated as Film 6 (non-magnetic) or Film 7 (magnetic), as for FIG.28A but at scan rates of 100 mV/s and 20 mV/s, respectively. Enhancedcurrent for magnetic Film 7, as compared with non-magnetic Film 6, canalso be seen in FIGS. 28B and 28C. The effect is particularly wellillustrated in FIG. 28C (20 mV/s scan rate) in which case the oxidationwave is very obvious for the electrode coated with the magneticcomposite film at −300 mV, but is completely absent for both the bareelectrode and the electrode coated with the non-magnetic composite.

Further evidence that the magnetic modification of the electrodeprevents passivation is seen at +100 mV on the return sweep. Theelectrode coated with the magnetic composite exhibits a simple reversewave. In contrast, both the bare electrode and that modified with thenon-magnetic composite both exhibit a wave that first swings to negativecurrent and then swings to positive current. The latter type of wave isconsistent with the stripping of a passivation layer from the surface ofthe electrode, thereby allowing a chemical species that would otherwise(i.e. in the absence of a passivation layer) have been electrolyzed atlower potential (but was prevented from so doing by the passivationlayer) to undergo electrolysis once the passivation layer is strippedfrom the electrode.

There is some evidence that the electrolysis of ethanol at amagnetically modified electrode is chemically reversible, as indicatedby the backwave at −400 mV vs SCE. The fact that the best resolvedvoltammograms were obtained at low scan rates is a good indication thatelectrodes magnetically modified with composite coatings, according tothe present invention, will perform well in commercially valuableelectrochemical processes, such as in steady state fuel cellapplications. An electrode which resists, or is less susceptible to,passivation will provide higher power output for longer periods, ascompared with an electrode which is more susceptible to passivation.

FIG. 29A shows cyclic voltammetric data for ethanol oxidation (6 mMethanol in 0.1 M Na₂SO₄) using a bare platinum electrode, and usingplatinum electrodes bearing surface composites designated as Film 8(magnetic) or Film 9 (non-magnetic). The voltammograms were recorded ata scan rate of 500 mV/s. FIGS. 29 B and 29 C show cyclic voltammetricdata for ethanol oxidation (6 mM ethanol in 0.1 M Na₂SO₄) using a bareplatinum electrode, and using platinum electrodes bearing surfacecomposites designated as Film 9 (non-magnetic) or Film 8 (magnetic), asfor FIG. 29A but at scan rates of 100 mV/s and 20 mV/s, respectively.Again, it can be seen that the electrode coated with the magnetic film(Film 8) has much higher current than the electrode bearing thenon-magnetic film (Film 9). In the case of Film 9, it can be seen fromFIG. 29A-C that the electrode coated with this non-magnetic film has alarger current than the bare electrode, due to the relatively high % ofplatinized carbon in the film (cf. Film 6, FIG. 28A). Referring to FIG.29C, the voltammetric trace for the magnetic film has more peaks, ascompared with those for the non-magnetic film and for the bareelectrode. This may be due to the stabilization of intermediates ofethanol oxidation by the magnetic field associated with the magneticparticles in the film.

Taken as a whole, the data are consistent with magnetic modification ofelectrodes, according to the invention, for the prevention ofpassivation of electrodes. Compositions, apparatus, and methods of theinvention also allow for the direct reformation of a liquid fuel, suchas ethanol, at the surface of a magnetically modified electrode. Suchcompositions, apparatus, and methods are advantageous in a range ofapplications related to the development of electrochemical processeswhich proceed by either a free radical mechanism or a multielectrontransfer process, and in fuel cell applications.

Numerous and additional modifications, improvements, and variations ofthe present invention are possible in light of the above teachings. Itis therefore to be understood that the invention may be practicedotherwise than as specifically disclosed, and that the scope of theinvention is defined by the appended claims rather than by theembodiments presented above.

What is claimed is:
 1. A method of making an electrode having a surfacecoating of a magnetic composite, wherein the electrode resistspassivation, comprising the steps of: providing an electrode; casting acasting mixture onto the surface of the electrode, said casting mixturecomprising an ion exchange polymer, magnetic particles, and a solvent;and evaporating the solvent from the surface of the electrode to yieldan electrode having a surface coating of the magnetic composite, whereinthe resulting coated electrode resists passivation.
 2. The method ofclaim 1, further comprising the step of: after casting the castingmixture, arranging the electrode in an external magnetic field beforeevaporation of the solvent.
 3. The method of claim 2, further comprisingthe step of: removing the electrode from the external magnetic fieldafter evaporation of the solvent.
 4. The method of claim 1, wherein saidcasting step comprises casting a casting mixture further comprisingparticles containing a catalyst.
 5. The method of claim 4, wherein thestep of casting a casting mixture comprises platinum, platinum-coatedcarbon, platinum/ruthenium, ruthenium, palladium, rhodium, cobalt,nickel, a porphyrin, a platinum-iron alloy, a platinum-cobalt alloy, aplatinum-nickel alloy, a transition metal, or combinations thereof asthe catalyst.
 6. The method of claim 1, wherein said casting stepcomprises casting a casting mixture further comprising: carbon particleshaving a platinum catalyst disposed on the surface of the carbonparticles.
 7. The method of claim 6, wherein the step of casting acasting mixture comprises the platinum catalyst disposed on the surfaceof the carbon particles by from about 5% to about 99.99% by weight ofthe carbon particles as part of the casting mixture.
 8. The method ofclaim 6, wherein the step of casting a casting mixture comprisesmagnetic particles that have diameters in the range of from about 0.1 μmto about 50 μm.
 9. The method of claim 6, wherein the step of casting acasting mixture comprises magnetic particles that comprise from about 2%to about 90% by weight of magnetizable or magnetic material.
 10. Themethod of claim 1, wherein said providing an electrode step comprisesproviding an anode.
 11. The method of claim 1, wherein the step ofcasting a casting mixture comprises casting an ion exchange polymer thatcomprises from about 15% to about 99.99% by weight of the castingmixture.
 12. The method of claim 1, wherein the step of evaporating thesolvent comprises producing the surface coating with a thickness in therange of from about 0.5 μm to about 100 μm.
 13. The method of claim 1,wherein the step of casting a casting mixture comprises said castingmixture comprising an electron conductor, and said electron conductormay comprise carbon.
 14. A method of making an electrode having asurface coating of a magnetic composite, wherein the electrode resistspassivation, comprising the steps of: providing an electrode; forming asuspension comprising magnetic particles and a polymeric material in asolvent; depositing the suspension on the electrode; and evaporating thesolvent to form a magnetic composite coating on the electrode.
 15. Themethod of claim 14, wherein the step of forming a suspension comprisesmagnetic particles that comprise an iron oxide, a samarium cobalt, aneodymium alloy, nickel, cobalt, iron, neodymium iron boron, alanthanide, or combinations thereof.
 16. The method of claim 14, whereinthe step of forming a suspension comprises polymeric material that is anion exchange polymer.